Example usage for com.google.common.collect Maps.EntryTransformer transformEntry

Introduction

In this page you can find the example usage for com.google.common.collect Maps.EntryTransformer transformEntry.

Prototype

static <V2, K, V1> Entry<K, V2> transformEntry(final EntryTransformer<? super K, ? super V1, V2> transformer,
        final Entry<K, V1> entry) 

Source Link

Document

Returns a view of an entry transformed by the specified transformer.

Usage

From source file:edu.mit.streamjit.util.CollectionUtils.java

/**
 * Returns the union of the given maps, using the given function to merge
 * values for the same key.  The function is called for all keys with a list
 * of the values of the maps in the order the maps were given.  Maps that do
 * not contain the key are not represented in the list.  The function's
 * return value is used as the value in the union map.
 * TODO: the generics don't seem right here; I should be able to use e.g.
 * a Collection<Comparable> in place of List<Integer> for the middle arg.
 * Note that the above overload permits that and forwards to this one!
 * @param <K> the key type of the returned map
 * @param <V> the value type of the returned map
 * @param <X> the value type of the input map(s)
 * @param merger the function used to merge values for the same key
 * @param maps the maps/*from  w ww.  j  ava  2 s  .  c o m*/
 * @return a map containing all the keys in the given maps
 */
public static <K, V, X> ImmutableMap<K, V> union(
        Maps.EntryTransformer<? super K, ? super List<X>, ? extends V> merger,
        List<? extends Map<? extends K, ? extends X>> maps) {
    ImmutableSet.Builder<K> keys = ImmutableSet.builder();
    for (Map<? extends K, ? extends X> m : maps)
        keys.addAll(m.keySet());

    ImmutableMap.Builder<K, V> builder = ImmutableMap.builder();
    for (K k : keys.build()) {
        ImmutableList.Builder<X> values = ImmutableList.builder();
        for (Map<? extends K, ? extends X> m : maps)
            if (m.containsKey(k))
                values.add(m.get(k));
        builder.put(k, merger.transformEntry(k, values.build()));
    }
    return builder.build();
}

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