/*
 * 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 tech.tablesaw.api;

import it.unimi.dsi.fastutil.objects.Object2IntMap;
import it.unimi.dsi.fastutil.objects.Object2IntOpenHashMap;
import java.util.Map;
import tech.tablesaw.columns.Column;

/**
 * A column type that can be summarized, or serve as a grouping variable in cross tabs or other
 * aggregation operations.
 *
 * <p>The column data is generally discrete, however NumberColumn implements CategoricalColumn so
 * that it can be used to summarize when it contains ints. If you use it to summarize over a large
 * range of floating point numbers, you will likely run out of memory.
 *
 * <p>Supporting subtypes include: - StringColumn - BooleanColumn - DateColumn, - etc
 *
 * <p>DateTimeColumn is not included. TimeColumn can be converted to ints without loss of data, so
 * it does implement this interface
 */
public interface CategoricalColumn<T> extends Column<T> {

  default Table countByCategory() {

    final Table t = new Table("Column: " + name());
    final CategoricalColumn<?> categories = (CategoricalColumn<?>) type().create("Category");
    final IntColumn counts = IntColumn.create("Count");

    final Object2IntMap<String> valueToCount = new Object2IntOpenHashMap<>();

    for (int i = 0; i < size(); i++) {
      if (!isMissing(i)) {
        final String next = getString(i);
        if (valueToCount.containsKey(next)) {
          valueToCount.put(next, valueToCount.getInt(next) + 1);
        } else {
          valueToCount.put(next, 1);
        }
      }
    }
    for (Map.Entry<String, Integer> entry : valueToCount.object2IntEntrySet()) {
      categories.appendCell(entry.getKey());
      counts.append(entry.getValue());
    }
    if (countMissing() > 0) {
      categories.appendMissing();
      counts.append(countMissing());
    }
    t.addColumns(categories);
    t.addColumns(counts);
    return t;
  }
}

@@ -1444,16 +1444,206 @@
 n%3CT%3E %7B%0A%0A
+  /**%0A   * Returns a count of the number of elements in each category (i.e., the number of repetitions of%0A   * each value) TODO: This needs to be well tested, especially for IntColumn%0A   */%0A
   defaul

Update CategoricalColumn.java