/*
 * Copyright (C) 2009 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.common.collect;

import static com.google.common.base.Preconditions.checkArgument;
import static com.google.common.base.Preconditions.checkElementIndex;
import static com.google.common.base.Preconditions.checkNotNull;

import com.google.common.annotations.Beta;
import com.google.common.annotations.GwtCompatible;
import com.google.common.annotations.GwtIncompatible;
import com.google.common.base.Objects;
import com.google.common.collect.Maps.IteratorBasedAbstractMap;
import com.google.errorprone.annotations.CanIgnoreReturnValue;
import com.google.j2objc.annotations.WeakOuter;
import java.io.Serializable;
import java.lang.reflect.Array;
import java.util.Arrays;
import java.util.Collection;
import java.util.Iterator;
import java.util.Map;
import java.util.Set;
import java.util.Spliterator;
import org.checkerframework.checker.nullness.qual.MonotonicNonNull;
import org.checkerframework.checker.nullness.qual.Nullable;

Fixed-size Table implementation backed by a two-dimensional array. 
The allowed row and column keys must be supplied when the table is created. The table always
contains a mapping for every row key / column pair. The value corresponding to a given row and
column is null unless another value is provided.
The table's size is constant: the product of the number of supplied row keys and the number of supplied column keys. The remove and clear methods are not supported by the table or its views. The erase and eraseAll methods may be used instead. 
The ordering of the row and column keys provided when the table is constructed determines the iteration ordering across rows and columns in the table's views. None of the view iterators support Iterator.remove. If the table is modified after an iterator is created, the iterator remains valid. 
This class requires less memory than the HashBasedTable and TreeBasedTable implementations, except when the table is sparse. 
Null row keys or column keys are not permitted.
This class provides methods involving the underlying array structure, where the array indices correspond to the position of a row or column in the lists of allowed keys and values. See the at, set, toArray, rowKeyList, and columnKeyList methods for more details. 
Note that this implementation is not synchronized. If multiple threads access the same cell of an ArrayTable concurrently and one of the threads modifies its value, there is no guarantee that the new value will be fully visible to the other threads. To guarantee that modifications are visible, synchronize access to the table. Unlike other Table implementations, synchronization is unnecessary between a thread that writes to one cell and a thread that reads from another. 
See the Guava User Guide article on  Table.
Author:
Jared Levy
Since:
10.0/**
 * Fixed-size {@link Table} implementation backed by a two-dimensional array.
 *
 * <p>The allowed row and column keys must be supplied when the table is created. The table always
 * contains a mapping for every row key / column pair. The value corresponding to a given row and
 * column is null unless another value is provided.
 *
 * <p>The table's size is constant: the product of the number of supplied row keys and the number of
 * supplied column keys. The {@code remove} and {@code clear} methods are not supported by the table
 * or its views. The {@link #erase} and {@link #eraseAll} methods may be used instead.
 *
 * <p>The ordering of the row and column keys provided when the table is constructed determines the
 * iteration ordering across rows and columns in the table's views. None of the view iterators
 * support {@link Iterator#remove}. If the table is modified after an iterator is created, the
 * iterator remains valid.
 *
 * <p>This class requires less memory than the {@link HashBasedTable} and {@link TreeBasedTable}
 * implementations, except when the table is sparse.
 *
 * <p>Null row keys or column keys are not permitted.
 *
 * <p>This class provides methods involving the underlying array structure, where the array indices
 * correspond to the position of a row or column in the lists of allowed keys and values. See the
 * {@link #at}, {@link #set}, {@link #toArray}, {@link #rowKeyList}, and {@link #columnKeyList}
 * methods for more details.
 *
 * <p>Note that this implementation is not synchronized. If multiple threads access the same cell of
 * an {@code ArrayTable} concurrently and one of the threads modifies its value, there is no
 * guarantee that the new value will be fully visible to the other threads. To guarantee that
 * modifications are visible, synchronize access to the table. Unlike other {@code Table}
 * implementations, synchronization is unnecessary between a thread that writes to one cell and a
 * thread that reads from another.
 *
 * <p>See the Guava User Guide article on <a href=
 * "https://github.com/google/guava/wiki/NewCollectionTypesExplained#table"> {@code Table}</a>.
 *
 * @author Jared Levy
 * @since 10.0
 */
@Beta
@GwtCompatible(emulated = true)
public final class ArrayTable<R, C, V> extends AbstractTable<R, C, V> implements Serializable {

  
Creates an ArrayTable filled with null. 
Params:
rowKeys – row keys that may be stored in the generated table
columnKeys – column keys that may be stored in the generated table
Throws:
NullPointerException – if any of the provided keys is null
IllegalArgumentException – if rowKeys or columnKeys contains duplicates or if exactly one of rowKeys or columnKeys is empty./**
   * Creates an {@code ArrayTable} filled with {@code null}.
   *
   * @param rowKeys row keys that may be stored in the generated table
   * @param columnKeys column keys that may be stored in the generated table
   * @throws NullPointerException if any of the provided keys is null
   * @throws IllegalArgumentException if {@code rowKeys} or {@code columnKeys} contains duplicates
   *     or if exactly one of {@code rowKeys} or {@code columnKeys} is empty.
   */
  public static <R, C, V> ArrayTable<R, C, V> create(
      Iterable<? extends R> rowKeys, Iterable<? extends C> columnKeys) {
    return new ArrayTable<>(rowKeys, columnKeys);
  }

  /*
   * TODO(jlevy): Add factory methods taking an Enum class, instead of an
   * iterable, to specify the allowed row keys and/or column keys. Note that
   * custom serialization logic is needed to support different enum sizes during
   * serialization and deserialization.
   */

  
Creates an ArrayTable with the mappings in the provided table. 
If table includes a mapping with row key r and a separate mapping with column key c, the returned table contains a mapping with row key r and column key c. If that row key / column key pair in not in table, the pair maps to null in the generated table. 
The returned table allows subsequent put calls with the row keys in 
table.rowKeySet() and the column keys in table.columnKeySet(). Calling put with other keys leads to an IllegalArgumentException. 
The ordering of table.rowKeySet() and table.columnKeySet() determines the row and column iteration ordering of the returned table. 
Throws:
NullPointerException – if table has a null key/**
   * Creates an {@code ArrayTable} with the mappings in the provided table.
   *
   * <p>If {@code table} includes a mapping with row key {@code r} and a separate mapping with
   * column key {@code c}, the returned table contains a mapping with row key {@code r} and column
   * key {@code c}. If that row key / column key pair in not in {@code table}, the pair maps to
   * {@code null} in the generated table.
   *
   * <p>The returned table allows subsequent {@code put} calls with the row keys in {@code
   * table.rowKeySet()} and the column keys in {@code table.columnKeySet()}. Calling {@link #put}
   * with other keys leads to an {@code IllegalArgumentException}.
   *
   * <p>The ordering of {@code table.rowKeySet()} and {@code table.columnKeySet()} determines the
   * row and column iteration ordering of the returned table.
   *
   * @throws NullPointerException if {@code table} has a null key
   */
  public static <R, C, V> ArrayTable<R, C, V> create(Table<R, C, V> table) {
    return (table instanceof ArrayTable<?, ?, ?>)
        ? new ArrayTable<R, C, V>((ArrayTable<R, C, V>) table)
        : new ArrayTable<R, C, V>(table);
  }

  private final ImmutableList<R> rowList;
  private final ImmutableList<C> columnList;

  // TODO(jlevy): Add getters returning rowKeyToIndex and columnKeyToIndex?
  private final ImmutableMap<R, Integer> rowKeyToIndex;
  private final ImmutableMap<C, Integer> columnKeyToIndex;
  private final V[][] array;

  private ArrayTable(Iterable<? extends R> rowKeys, Iterable<? extends C> columnKeys) {
    this.rowList = ImmutableList.copyOf(rowKeys);
    this.columnList = ImmutableList.copyOf(columnKeys);
    checkArgument(rowList.isEmpty() == columnList.isEmpty());

    /*
     * TODO(jlevy): Support only one of rowKey / columnKey being empty? If we
     * do, when columnKeys is empty but rowKeys isn't, rowKeyList() can contain
     * elements but rowKeySet() will be empty and containsRow() won't
     * acknolwedge them.
     */
    rowKeyToIndex = Maps.indexMap(rowList);
    columnKeyToIndex = Maps.indexMap(columnList);

    @SuppressWarnings("unchecked")
    V[][] tmpArray = (V[][]) new Object[rowList.size()][columnList.size()];
    array = tmpArray;
    // Necessary because in GWT the arrays are initialized with "undefined" instead of null.
    eraseAll();
  }

  private ArrayTable(Table<R, C, V> table) {
    this(table.rowKeySet(), table.columnKeySet());
    putAll(table);
  }

  private ArrayTable(ArrayTable<R, C, V> table) {
    rowList = table.rowList;
    columnList = table.columnList;
    rowKeyToIndex = table.rowKeyToIndex;
    columnKeyToIndex = table.columnKeyToIndex;
    @SuppressWarnings("unchecked")
    V[][] copy = (V[][]) new Object[rowList.size()][columnList.size()];
    array = copy;
    for (int i = 0; i < rowList.size(); i++) {
      System.arraycopy(table.array[i], 0, copy[i], 0, table.array[i].length);
    }
  }

  private abstract static class ArrayMap<K, V> extends IteratorBasedAbstractMap<K, V> {
    private final ImmutableMap<K, Integer> keyIndex;

    private ArrayMap(ImmutableMap<K, Integer> keyIndex) {
      this.keyIndex = keyIndex;
    }

    @Override
    public Set<K> keySet() {
      return keyIndex.keySet();
    }

    K getKey(int index) {
      return keyIndex.keySet().asList().get(index);
    }

    abstract String getKeyRole();

    abstract @Nullable V getValue(int index);

    abstract @Nullable V setValue(int index, V newValue);

    @Override
    public int size() {
      return keyIndex.size();
    }

    @Override
    public boolean isEmpty() {
      return keyIndex.isEmpty();
    }

    Entry<K, V> getEntry(final int index) {
      checkElementIndex(index, size());
      return new AbstractMapEntry<K, V>() {
        @Override
        public K getKey() {
          return ArrayMap.this.getKey(index);
        }

        @Override
        public V getValue() {
          return ArrayMap.this.getValue(index);
        }

        @Override
        public V setValue(V value) {
          return ArrayMap.this.setValue(index, value);
        }
      };
    }

    @Override
    Iterator<Entry<K, V>> entryIterator() {
      return new AbstractIndexedListIterator<Entry<K, V>>(size()) {
        @Override
        protected Entry<K, V> get(final int index) {
          return getEntry(index);
        }
      };
    }

    @Override
    Spliterator<Entry<K, V>> entrySpliterator() {
      return CollectSpliterators.indexed(size(), Spliterator.ORDERED, this::getEntry);
    }

    // TODO(lowasser): consider an optimized values() implementation

    @Override
    public boolean containsKey(@Nullable Object key) {
      return keyIndex.containsKey(key);
    }

    @Override
    public V get(@Nullable Object key) {
      Integer index = keyIndex.get(key);
      if (index == null) {
        return null;
      } else {
        return getValue(index);
      }
    }

    @Override
    public V put(K key, V value) {
      Integer index = keyIndex.get(key);
      if (index == null) {
        throw new IllegalArgumentException(
            getKeyRole() + " " + key + " not in " + keyIndex.keySet());
      }
      return setValue(index, value);
    }

    @Override
    public V remove(Object key) {
      throw new UnsupportedOperationException();
    }

    @Override
    public void clear() {
      throw new UnsupportedOperationException();
    }
  }

  
Returns, as an immutable list, the row keys provided when the table was constructed, including
those that are mapped to null values only.
/**
   * Returns, as an immutable list, the row keys provided when the table was constructed, including
   * those that are mapped to null values only.
   */
  public ImmutableList<R> rowKeyList() {
    return rowList;
  }

  
Returns, as an immutable list, the column keys provided when the table was constructed,
including those that are mapped to null values only.
/**
   * Returns, as an immutable list, the column keys provided when the table was constructed,
   * including those that are mapped to null values only.
   */
  public ImmutableList<C> columnKeyList() {
    return columnList;
  }

  
Returns the value corresponding to the specified row and column indices. The same value is returned by get(rowKeyList().get(rowIndex), columnKeyList().get(columnIndex)), but this method runs more quickly. 
Params:
rowIndex – position of the row key in rowKeyList()
columnIndex – position of the row key in columnKeyList()
Throws:
IndexOutOfBoundsException – if either index is negative, rowIndex is greater than or equal to the number of allowed row keys, or columnIndex is greater than or equal to the number of allowed column keys
Returns:
the value with the specified row and column/**
   * Returns the value corresponding to the specified row and column indices. The same value is
   * returned by {@code get(rowKeyList().get(rowIndex), columnKeyList().get(columnIndex))}, but this
   * method runs more quickly.
   *
   * @param rowIndex position of the row key in {@link #rowKeyList()}
   * @param columnIndex position of the row key in {@link #columnKeyList()}
   * @return the value with the specified row and column
   * @throws IndexOutOfBoundsException if either index is negative, {@code rowIndex} is greater than
   *     or equal to the number of allowed row keys, or {@code columnIndex} is greater than or equal
   *     to the number of allowed column keys
   */
  public V at(int rowIndex, int columnIndex) {
    // In GWT array access never throws IndexOutOfBoundsException.
    checkElementIndex(rowIndex, rowList.size());
    checkElementIndex(columnIndex, columnList.size());
    return array[rowIndex][columnIndex];
  }

  
Associates value with the specified row and column indices. The logic 
put(rowKeyList().get(rowIndex), columnKeyList().get(columnIndex), value) has the same behavior, but this method runs more quickly. 
Params:
rowIndex – position of the row key in rowKeyList()
columnIndex – position of the row key in columnKeyList()
value – value to store in the table
Throws:
IndexOutOfBoundsException – if either index is negative, rowIndex is greater than or equal to the number of allowed row keys, or columnIndex is greater than or equal to the number of allowed column keys
Returns:
the previous value with the specified row and column/**
   * Associates {@code value} with the specified row and column indices. The logic {@code
   * put(rowKeyList().get(rowIndex), columnKeyList().get(columnIndex), value)} has the same
   * behavior, but this method runs more quickly.
   *
   * @param rowIndex position of the row key in {@link #rowKeyList()}
   * @param columnIndex position of the row key in {@link #columnKeyList()}
   * @param value value to store in the table
   * @return the previous value with the specified row and column
   * @throws IndexOutOfBoundsException if either index is negative, {@code rowIndex} is greater than
   *     or equal to the number of allowed row keys, or {@code columnIndex} is greater than or equal
   *     to the number of allowed column keys
   */
  @CanIgnoreReturnValue
  public V set(int rowIndex, int columnIndex, @Nullable V value) {
    // In GWT array access never throws IndexOutOfBoundsException.
    checkElementIndex(rowIndex, rowList.size());
    checkElementIndex(columnIndex, columnList.size());
    V oldValue = array[rowIndex][columnIndex];
    array[rowIndex][columnIndex] = value;
    return oldValue;
  }

  
Returns a two-dimensional array with the table contents. The row and column indices correspond
to the positions of the row and column in the iterables provided during table construction. If
the table lacks a mapping for a given row and column, the corresponding array element is null.
Subsequent table changes will not modify the array, and vice versa.
Params:
valueClass – class of values stored in the returned array/**
   * Returns a two-dimensional array with the table contents. The row and column indices correspond
   * to the positions of the row and column in the iterables provided during table construction. If
   * the table lacks a mapping for a given row and column, the corresponding array element is null.
   *
   * <p>Subsequent table changes will not modify the array, and vice versa.
   *
   * @param valueClass class of values stored in the returned array
   */
  @GwtIncompatible // reflection
  public V[][] toArray(Class<V> valueClass) {
    @SuppressWarnings("unchecked") // TODO: safe?
    V[][] copy = (V[][]) Array.newInstance(valueClass, rowList.size(), columnList.size());
    for (int i = 0; i < rowList.size(); i++) {
      System.arraycopy(array[i], 0, copy[i], 0, array[i].length);
    }
    return copy;
  }

  
Not supported. Use eraseAll instead. 
Throws:
UnsupportedOperationException – always
Deprecated:
Use eraseAll/**
   * Not supported. Use {@link #eraseAll} instead.
   *
   * @throws UnsupportedOperationException always
   * @deprecated Use {@link #eraseAll}
   */
  @Override
  @Deprecated
  public void clear() {
    throw new UnsupportedOperationException();
  }

  
Associates the value null with every pair of allowed row and column keys. /** Associates the value {@code null} with every pair of allowed row and column keys. */
  public void eraseAll() {
    for (V[] row : array) {
      Arrays.fill(row, null);
    }
  }

  
Returns true if the provided keys are among the keys provided when the table was constructed. /**
   * Returns {@code true} if the provided keys are among the keys provided when the table was
   * constructed.
   */
  @Override
  public boolean contains(@Nullable Object rowKey, @Nullable Object columnKey) {
    return containsRow(rowKey) && containsColumn(columnKey);
  }

  
Returns true if the provided column key is among the column keys provided when the table was constructed. /**
   * Returns {@code true} if the provided column key is among the column keys provided when the
   * table was constructed.
   */
  @Override
  public boolean containsColumn(@Nullable Object columnKey) {
    return columnKeyToIndex.containsKey(columnKey);
  }

  
Returns true if the provided row key is among the row keys provided when the table was constructed. /**
   * Returns {@code true} if the provided row key is among the row keys provided when the table was
   * constructed.
   */
  @Override
  public boolean containsRow(@Nullable Object rowKey) {
    return rowKeyToIndex.containsKey(rowKey);
  }

  @Override
  public boolean containsValue(@Nullable Object value) {
    for (V[] row : array) {
      for (V element : row) {
        if (Objects.equal(value, element)) {
          return true;
        }
      }
    }
    return false;
  }

  @Override
  public V get(@Nullable Object rowKey, @Nullable Object columnKey) {
    Integer rowIndex = rowKeyToIndex.get(rowKey);
    Integer columnIndex = columnKeyToIndex.get(columnKey);
    return (rowIndex == null || columnIndex == null) ? null : at(rowIndex, columnIndex);
  }

  
Returns true if rowKeyList().size == 0 or columnKeyList().size() == 0. /**
   * Returns {@code true} if {@code rowKeyList().size == 0} or {@code columnKeyList().size() == 0}.
   */
  @Override
  public boolean isEmpty() {
    return rowList.isEmpty() || columnList.isEmpty();
  }

  
{@inheritDoc}
Throws:
IllegalArgumentException – if rowKey is not in rowKeySet() or 
    columnKey is not in columnKeySet()./**
   * {@inheritDoc}
   *
   * @throws IllegalArgumentException if {@code rowKey} is not in {@link #rowKeySet()} or {@code
   *     columnKey} is not in {@link #columnKeySet()}.
   */
  @CanIgnoreReturnValue
  @Override
  public V put(R rowKey, C columnKey, @Nullable V value) {
    checkNotNull(rowKey);
    checkNotNull(columnKey);
    Integer rowIndex = rowKeyToIndex.get(rowKey);
    checkArgument(rowIndex != null, "Row %s not in %s", rowKey, rowList);
    Integer columnIndex = columnKeyToIndex.get(columnKey);
    checkArgument(columnIndex != null, "Column %s not in %s", columnKey, columnList);
    return set(rowIndex, columnIndex, value);
  }

  /*
   * TODO(jlevy): Consider creating a merge() method, similar to putAll() but
   * copying non-null values only.
   */

  
{@inheritDoc}
If table is an ArrayTable, its null values will be stored in this table, possibly replacing values that were previously non-null. 
Throws:
NullPointerException – if table has a null key
IllegalArgumentException – if any of the provided table's row keys or column keys is not in rowKeySet() or columnKeySet()/**
   * {@inheritDoc}
   *
   * <p>If {@code table} is an {@code ArrayTable}, its null values will be stored in this table,
   * possibly replacing values that were previously non-null.
   *
   * @throws NullPointerException if {@code table} has a null key
   * @throws IllegalArgumentException if any of the provided table's row keys or column keys is not
   *     in {@link #rowKeySet()} or {@link #columnKeySet()}
   */
  @Override
  public void putAll(Table<? extends R, ? extends C, ? extends V> table) {
    super.putAll(table);
  }

  
Not supported. Use erase instead. 
Throws:
UnsupportedOperationException – always
Deprecated:
Use erase/**
   * Not supported. Use {@link #erase} instead.
   *
   * @throws UnsupportedOperationException always
   * @deprecated Use {@link #erase}
   */
  @CanIgnoreReturnValue
  @Override
  @Deprecated
  public V remove(Object rowKey, Object columnKey) {
    throw new UnsupportedOperationException();
  }

  
Associates the value null with the specified keys, assuming both keys are valid. If either key is null or isn't among the keys provided during construction, this method has no effect. 
This method is equivalent to put(rowKey, columnKey, null) when both provided keys are valid. 
Params:
rowKey – row key of mapping to be erased
columnKey – column key of mapping to be erased
Returns:
the value previously associated with the keys, or null if no mapping existed for the keys/**
   * Associates the value {@code null} with the specified keys, assuming both keys are valid. If
   * either key is null or isn't among the keys provided during construction, this method has no
   * effect.
   *
   * <p>This method is equivalent to {@code put(rowKey, columnKey, null)} when both provided keys
   * are valid.
   *
   * @param rowKey row key of mapping to be erased
   * @param columnKey column key of mapping to be erased
   * @return the value previously associated with the keys, or {@code null} if no mapping existed
   *     for the keys
   */
  @CanIgnoreReturnValue
  public V erase(@Nullable Object rowKey, @Nullable Object columnKey) {
    Integer rowIndex = rowKeyToIndex.get(rowKey);
    Integer columnIndex = columnKeyToIndex.get(columnKey);
    if (rowIndex == null || columnIndex == null) {
      return null;
    }
    return set(rowIndex, columnIndex, null);
  }

  // TODO(jlevy): Add eraseRow and eraseColumn methods?

  @Override
  public int size() {
    return rowList.size() * columnList.size();
  }

  
Returns an unmodifiable set of all row key / column key / value triplets. Changes to the table
will update the returned set.
The returned set's iterator traverses the mappings with the first row key, the mappings with
the second row key, and so on.
The value in the returned cells may change if the table subsequently changes.
Returns:
set of table cells consisting of row key / column key / value triplets/**
   * Returns an unmodifiable set of all row key / column key / value triplets. Changes to the table
   * will update the returned set.
   *
   * <p>The returned set's iterator traverses the mappings with the first row key, the mappings with
   * the second row key, and so on.
   *
   * <p>The value in the returned cells may change if the table subsequently changes.
   *
   * @return set of table cells consisting of row key / column key / value triplets
   */
  @Override
  public Set<Cell<R, C, V>> cellSet() {
    return super.cellSet();
  }

  @Override
  Iterator<Cell<R, C, V>> cellIterator() {
    return new AbstractIndexedListIterator<Cell<R, C, V>>(size()) {
      @Override
      protected Cell<R, C, V> get(final int index) {
        return getCell(index);
      }
    };
  }

  @Override
  Spliterator<Cell<R, C, V>> cellSpliterator() {
    return CollectSpliterators.indexed(
        size(), Spliterator.ORDERED | Spliterator.NONNULL | Spliterator.DISTINCT, this::getCell);
  }

  private Cell<R, C, V> getCell(final int index) {
    return new Tables.AbstractCell<R, C, V>() {
      final int rowIndex = index / columnList.size();
      final int columnIndex = index % columnList.size();

      @Override
      public R getRowKey() {
        return rowList.get(rowIndex);
      }

      @Override
      public C getColumnKey() {
        return columnList.get(columnIndex);
      }

      @Override
      public V getValue() {
        return at(rowIndex, columnIndex);
      }
    };
  }

  private V getValue(int index) {
    int rowIndex = index / columnList.size();
    int columnIndex = index % columnList.size();
    return at(rowIndex, columnIndex);
  }

  
Returns a view of all mappings that have the given column key. If the column key isn't in columnKeySet(), an empty immutable map is returned. 
Otherwise, for each row key in rowKeySet(), the returned map associates the row key with the corresponding value in the table. Changes to the returned map will update the underlying table, and vice versa. 
Params:
columnKey – key of column to search for in the table
Returns:
the corresponding map from row keys to values/**
   * Returns a view of all mappings that have the given column key. If the column key isn't in
   * {@link #columnKeySet()}, an empty immutable map is returned.
   *
   * <p>Otherwise, for each row key in {@link #rowKeySet()}, the returned map associates the row key
   * with the corresponding value in the table. Changes to the returned map will update the
   * underlying table, and vice versa.
   *
   * @param columnKey key of column to search for in the table
   * @return the corresponding map from row keys to values
   */
  @Override
  public Map<R, V> column(C columnKey) {
    checkNotNull(columnKey);
    Integer columnIndex = columnKeyToIndex.get(columnKey);
    return (columnIndex == null) ? ImmutableMap.<R, V>of() : new Column(columnIndex);
  }

  private class Column extends ArrayMap<R, V> {
    final int columnIndex;

    Column(int columnIndex) {
      super(rowKeyToIndex);
      this.columnIndex = columnIndex;
    }

    @Override
    String getKeyRole() {
      return "Row";
    }

    @Override
    V getValue(int index) {
      return at(index, columnIndex);
    }

    @Override
    V setValue(int index, V newValue) {
      return set(index, columnIndex, newValue);
    }
  }

  
Returns an immutable set of the valid column keys, including those that are associated with
null values only.
Returns:
immutable set of column keys/**
   * Returns an immutable set of the valid column keys, including those that are associated with
   * null values only.
   *
   * @return immutable set of column keys
   */
  @Override
  public ImmutableSet<C> columnKeySet() {
    return columnKeyToIndex.keySet();
  }

  private transient @MonotonicNonNull ColumnMap columnMap;

  @Override
  public Map<C, Map<R, V>> columnMap() {
    ColumnMap map = columnMap;
    return (map == null) ? columnMap = new ColumnMap() : map;
  }

  @WeakOuter
  private class ColumnMap extends ArrayMap<C, Map<R, V>> {
    private ColumnMap() {
      super(columnKeyToIndex);
    }

    @Override
    String getKeyRole() {
      return "Column";
    }

    @Override
    Map<R, V> getValue(int index) {
      return new Column(index);
    }

    @Override
    Map<R, V> setValue(int index, Map<R, V> newValue) {
      throw new UnsupportedOperationException();
    }

    @Override
    public Map<R, V> put(C key, Map<R, V> value) {
      throw new UnsupportedOperationException();
    }
  }

  
Returns a view of all mappings that have the given row key. If the row key isn't in rowKeySet(), an empty immutable map is returned. 
Otherwise, for each column key in columnKeySet(), the returned map associates the column key with the corresponding value in the table. Changes to the returned map will update the underlying table, and vice versa. 
Params:
rowKey – key of row to search for in the table
Returns:
the corresponding map from column keys to values/**
   * Returns a view of all mappings that have the given row key. If the row key isn't in {@link
   * #rowKeySet()}, an empty immutable map is returned.
   *
   * <p>Otherwise, for each column key in {@link #columnKeySet()}, the returned map associates the
   * column key with the corresponding value in the table. Changes to the returned map will update
   * the underlying table, and vice versa.
   *
   * @param rowKey key of row to search for in the table
   * @return the corresponding map from column keys to values
   */
  @Override
  public Map<C, V> row(R rowKey) {
    checkNotNull(rowKey);
    Integer rowIndex = rowKeyToIndex.get(rowKey);
    return (rowIndex == null) ? ImmutableMap.<C, V>of() : new Row(rowIndex);
  }

  private class Row extends ArrayMap<C, V> {
    final int rowIndex;

    Row(int rowIndex) {
      super(columnKeyToIndex);
      this.rowIndex = rowIndex;
    }

    @Override
    String getKeyRole() {
      return "Column";
    }

    @Override
    V getValue(int index) {
      return at(rowIndex, index);
    }

    @Override
    V setValue(int index, V newValue) {
      return set(rowIndex, index, newValue);
    }
  }

  
Returns an immutable set of the valid row keys, including those that are associated with null
values only.
Returns:
immutable set of row keys/**
   * Returns an immutable set of the valid row keys, including those that are associated with null
   * values only.
   *
   * @return immutable set of row keys
   */
  @Override
  public ImmutableSet<R> rowKeySet() {
    return rowKeyToIndex.keySet();
  }

  private transient @MonotonicNonNull RowMap rowMap;

  @Override
  public Map<R, Map<C, V>> rowMap() {
    RowMap map = rowMap;
    return (map == null) ? rowMap = new RowMap() : map;
  }

  @WeakOuter
  private class RowMap extends ArrayMap<R, Map<C, V>> {
    private RowMap() {
      super(rowKeyToIndex);
    }

    @Override
    String getKeyRole() {
      return "Row";
    }

    @Override
    Map<C, V> getValue(int index) {
      return new Row(index);
    }

    @Override
    Map<C, V> setValue(int index, Map<C, V> newValue) {
      throw new UnsupportedOperationException();
    }

    @Override
    public Map<C, V> put(R key, Map<C, V> value) {
      throw new UnsupportedOperationException();
    }
  }

  
Returns an unmodifiable collection of all values, which may contain duplicates. Changes to the
table will update the returned collection.
The returned collection's iterator traverses the values of the first row key, the values of
the second row key, and so on.
Returns:
collection of values/**
   * Returns an unmodifiable collection of all values, which may contain duplicates. Changes to the
   * table will update the returned collection.
   *
   * <p>The returned collection's iterator traverses the values of the first row key, the values of
   * the second row key, and so on.
   *
   * @return collection of values
   */
  @Override
  public Collection<V> values() {
    return super.values();
  }

  @Override
  Iterator<V> valuesIterator() {
    return new AbstractIndexedListIterator<V>(size()) {
      @Override
      protected V get(int index) {
        return getValue(index);
      }
    };
  }

  @Override
  Spliterator<V> valuesSpliterator() {
    return CollectSpliterators.indexed(size(), Spliterator.ORDERED, this::getValue);
  }

  private static final long serialVersionUID = 0;
}