Added U.associateBy(iterable, func)

Author: javadev

src/main/java/com/github/underscore/U.java

@@ -367,6 +367,11 @@ public <F> Chain<Map<F, List<T>>> groupBy(final Function<T, F> func) {
             return new Chain<>(Underscore.groupBy(value(), func));
         }
 
+        @Override
+        public <F> Chain<Map<F, T>> associateBy(final Function<T, F> func) {
+            return new Chain<>(Underscore.associateBy(value(), func));
+        }
+
         @Override
         public <F> Chain<Map<F, Optional<T>>> groupBy(
                 final Function<T, F> func, final BinaryOperator<T> binaryOperator) {

src/main/java/com/github/underscore/Underscore.java

@@ -1046,6 +1046,21 @@ public <K, E> Map<K, Optional<E>> groupBy(
         return groupBy((Iterable<E>) iterable, func, binaryOperator);
     }
 
+    public static <K, E> Map<K, E> associateBy(
+            final Iterable<E> iterable, final Function<E, K> func) {
+        final Map<K, E> retVal = newLinkedHashMap();
+        for (E e : iterable) {
+            final K key = func.apply(e);
+            retVal.putIfAbsent(key, e);
+        }
+        return retVal;
+    }
+
+    @SuppressWarnings("unchecked")
+    public <K, E> Map<K, E> associateBy(final Function<E, K> func) {
+        return associateBy((Iterable<E>) iterable, func);
+    }
+
     @SuppressWarnings("unchecked")
     public static <K, E> Map<K, List<E>> indexBy(
             final Iterable<E> iterable, final String property) {
@@ -3000,6 +3015,10 @@ public <F> Chain<Map<F, List<T>>> groupBy(final Function<T, F> func) {
             return new Chain<>(Underscore.groupBy(list, func));
         }
 
+        public <F> Chain<Map<F, T>> associateBy(final Function<T, F> func) {
+            return new Chain<>(Underscore.associateBy(list, func));
+        }
+
         public <F> Chain<Map<F, Optional<T>>> groupBy(
                 final Function<T, F> func, final BinaryOperator<T> binaryOperator) {
             return new Chain<>(Underscore.groupBy(list, func, binaryOperator));

src/test/java/com/github/underscore/CollectionsTest.java

@@ -1436,6 +1436,26 @@ void groupBy() {
         assertEquals("{1.0=[1.3], 2.0=[2.1, 2.4]}", resultChain.toString());
     }
 
+    /*
+    _.associateBy([1.3, 2.1, 2.4], function(num){ return Math.floor(num); });
+    => {1: [1.3], 2: [2.1, 2.4]}
+    */
+    @Test
+    @SuppressWarnings("unchecked")
+    void associateBy() {
+        final Map<Double, Double> result =
+                Underscore.associateBy(asList(1.3, 2.1, 2.4), Math::floor);
+        assertEquals("{1.0=1.3, 2.0=2.1}", result.toString());
+        final Map<Double, Double> resultObj =
+                new Underscore(asList(1.3, 2.1, 2.4))
+                        .associateBy((Function<Double, Double>) Math::floor);
+        assertEquals("{1.0=1.3, 2.0=2.1}", resultObj.toString());
+        final Map<Double, Double> resultChain =
+                (Map<Double, Double>)
+                        Underscore.chain(asList(1.3, 2.1, 2.4)).associateBy(Math::floor).item();
+        assertEquals("{1.0=1.3, 2.0=2.1}", resultChain.toString());
+    }
+
     /*
     _.groupBy([1.3, 2.1, 2.4], function(num){ return Math.floor(num); });
     => {1: [1.3], 2: [2.1, 2.4]}

src/test/java/com/github/underscore/LodashTest.java

@@ -1780,6 +1780,7 @@ void chain() {
         U.chain(new Integer[] {0}).sortBy(value -> value);
         U.chain(new LinkedHashMap<Integer, Integer>().entrySet()).sortBy("");
         U.chain(new Integer[] {0}).groupBy(value -> value);
+        U.chain(new Integer[] {0}).associateBy(value -> value);
         U.chain(new Integer[] {0}).groupBy(num -> num, (a, b) -> a);
         U.chain(new Integer[] {0}).indexBy("");
         U.chain(new Integer[] {0}).countBy(value -> value);