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Sorting maps by value.
package com.comphenix.testing;
import java.util.Comparator;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
import com.google.common.base.Function;
import com.google.common.collect.Iterables;
import com.google.common.collect.Ordering;
@SuppressWarnings("rawtypes")
public class MapSorting {
// Building block - extract key from entry
private static final Function EXTRACT_KEY =
new Function<Entry<Object, Object>, Object>() {
public Object apply(Entry<Object, Object> input) {
return input.getKey();
}
};
// Same as above, only we extract the value
private static final Function EXTRACT_VALUE =
new Function<Entry<Object, Object>, Object>() {
public Object apply(Entry<Object, Object> input) {
return input.getValue();
}
};
/**
* Sort the given map by the value in each entry.
* @param map - map of comparable values.
* @return A new list with the sort result.
*/
public static <T, V extends Comparable<V>> List<Entry<T, V>> sortedValues(Map<T, V> map) {
return sortedValues(map, Ordering.<V>natural());
}
/**
* Sort the given map by the value in each entry.
* @param map - map of comparable values.
* @param valueComparator - object for comparing each values.
* @return A new list with the sort result.
*/
public static <T, V> List<Entry<T, V>> sortedValues(Map<T, V> map, Comparator<V> valueComparator) {
return Ordering.from(valueComparator).onResultOf(MapSorting.<T, V>extractValue()).sortedCopy(map.entrySet());
}
/**
* Retrieve every key in the entry list in order.
* @param entryList - the entry list.
* @return Every key in order.
*/
public static <T, V> Iterable<T> keys(List<Entry<T, V>> entryList) {
return Iterables.transform(entryList, MapSorting.<T, V>extractKey());
}
/**
* Retrieve every value in the entry list in order.
* @param entryList - the entry list.
* @return Every value in order.
*/
public static <T, V> Iterable<V> values(List<Entry<T, V>> entryList) {
return Iterables.transform(entryList, MapSorting.<T, V>extractValue());
}
@SuppressWarnings("unchecked")
private static <T, V> Function<Entry<T, V>, T> extractKey() {
return EXTRACT_KEY;
}
@SuppressWarnings("unchecked")
private static <T, V> Function<Entry<T, V>, V> extractValue() {
return EXTRACT_VALUE;
}
}
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