the-algorithm/src/java/com/twitter/search/common/util/earlybird/ResultsUtil.java

package com.twitter.search.common.util.earlybird;

import java.util.Map;

import com.google.common.base.Function;
import com.google.common.collect.Iterables;
import com.google.common.collect.Maps;

/**
 * Utility class used to help merging results.
 */
public final class ResultsUtil {
  private ResultsUtil() { }

  /**
   * Aggregate a list of responses in the following way.
   * 1. For each response, mapGetter can turn the response into a map.
   * 2. Dump all entries from the above map into a "total" map, which accumulates entries from
   *    all the responses.
   */
  public static <T, V> Map<T, Integer> aggregateCountMap(
          Iterable<V> responses,
          Function<V, Map<T, Integer>> mapGetter) {
    Map<T, Integer> total = Maps.newHashMap();
    for (Map<T, Integer> map : Iterables.transform(responses, mapGetter)) {
      if (map != null) {
        for (Map.Entry<T, Integer> entry : map.entrySet()) {
          T key = entry.getKey();
          total.put(key, total.containsKey(key)
              ? total.get(key) + entry.getValue() : entry.getValue());
        }
      }
    }
    return total;
  }
}