io.druid.query.aggregation.cardinality.types.StringCardinalityAggregatorColumnSelectorStrategy.java Source code

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Here is the source code for io.druid.query.aggregation.cardinality.types.StringCardinalityAggregatorColumnSelectorStrategy.java

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/*
 * Licensed to Metamarkets Group Inc. (Metamarkets) under one
 * or more contributor license agreements. See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership. Metamarkets licenses this file
 * to you 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 io.druid.query.aggregation.cardinality.types;

import com.google.common.hash.Hasher;
import io.druid.hll.HyperLogLogCollector;
import io.druid.query.aggregation.cardinality.CardinalityAggregator;
import io.druid.segment.DimensionSelector;
import io.druid.segment.data.IndexedInts;

import java.util.Arrays;

public class StringCardinalityAggregatorColumnSelectorStrategy
        implements CardinalityAggregatorColumnSelectorStrategy<DimensionSelector> {
    public static final String CARDINALITY_AGG_NULL_STRING = "\u0000";
    public static final char CARDINALITY_AGG_SEPARATOR = '\u0001';

    @Override
    public void hashRow(DimensionSelector dimSelector, Hasher hasher) {
        final IndexedInts row = dimSelector.getRow();
        final int size = row.size();
        // nothing to add to hasher if size == 0, only handle size == 1 and size != 0 cases.
        if (size == 1) {
            final String value = dimSelector.lookupName(row.get(0));
            hasher.putUnencodedChars(nullToSpecial(value));
        } else if (size != 0) {
            final String[] values = new String[size];
            for (int i = 0; i < size; ++i) {
                final String value = dimSelector.lookupName(row.get(i));
                values[i] = nullToSpecial(value);
            }
            // Values need to be sorted to ensure consistent multi-value ordering across different segments
            Arrays.sort(values);
            for (int i = 0; i < size; ++i) {
                if (i != 0) {
                    hasher.putChar(CARDINALITY_AGG_SEPARATOR);
                }
                hasher.putUnencodedChars(values[i]);
            }
        }
    }

    @Override
    public void hashValues(DimensionSelector dimSelector, HyperLogLogCollector collector) {
        IndexedInts row = dimSelector.getRow();
        for (int i = 0; i < row.size(); i++) {
            int index = row.get(i);
            final String value = dimSelector.lookupName(index);
            collector.add(CardinalityAggregator.hashFn.hashUnencodedChars(nullToSpecial(value)).asBytes());
        }
    }

    private String nullToSpecial(String value) {
        return value == null ? CARDINALITY_AGG_NULL_STRING : value;
    }
}