java-recipe-manager/src/main/lombok/org/leumasjaffe/recipe/util/Collator.java

package org.leumasjaffe.recipe.util;

import java.util.Collection;
import java.util.HashMap;
import java.util.Map;
import java.util.function.BinaryOperator;
import java.util.function.Function;
import java.util.stream.Stream;

import lombok.experimental.UtilityClass;

@UtilityClass
public class Collator {
	public <T> Collection<T> collateBy(final Stream<T> stream, final Function<T, String> getKey,
			final BinaryOperator<T> folder) {
		final Map<String, T> map = new HashMap<>();
        stream.forEach(value -> {
        	final String key = getKey.apply(value);
            map.computeIfPresent(key, (k, v) -> folder.apply(v, value));
            map.computeIfAbsent(key, k -> value);
        });
        return map.values();
	}
}