Add top-level collection-manipulation functions.

test/functions_test.dart

+// Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import "package:test/test.dart";
+
+import "package:collection/collection.dart";
+
+void main() {
+  group("mapMap()", () {
+    test("with an empty map returns an empty map", () {
+      expect(
+          mapMap({},
+              key: expectAsync((_, __) {}, count: 0),
+              value: expectAsync((_, __) {}, count: 0)),
+          isEmpty);
+    });
+
+    test("with no callbacks, returns a copy of the map", () {
+      var map = {"foo": 1, "bar": 2};
+      var result = mapMap(map);
+      expect(result, equals({"foo": 1, "bar": 2}));
+
+      // The resulting map should be a copy.
+      result["foo"] = 3;
+      expect(map, equals({"foo": 1, "bar": 2}));
+    });
+
+    test("maps the map's keys", () {
+      expect(mapMap({"foo": 1, "bar": 2}, key: (key, value) => key[value]),
+          equals({"o": 1, "r": 2}));
+    });
+
+    test("maps the map's values", () {
+      expect(mapMap({"foo": 1, "bar": 2}, value: (key, value) => key[value]),
+          equals({"foo": "o", "bar": "r"}));
+    });
+
+    test("maps both the map's keys and values", () {
+      expect(
+          mapMap({"foo": 1, "bar": 2},
+              key: (key, value) => "$key$value",
+              value: (key, value) => key[value]),
+          equals({"foo1": "o", "bar2": "r"}));
+    });
+  });
+
+  group("mergeMaps()", () {
+    test("with empty maps returns an empty map", () {
+      expect(mergeMaps({}, {}, value: expectAsync((_, __) {}, count: 0)),
+          isEmpty);
+    });
+
+    test("returns a map with all values in both input maps", () {
+      expect(mergeMaps({"foo": 1, "bar": 2}, {"baz": 3, "qux": 4}),
+          equals({"foo": 1, "bar": 2, "baz": 3, "qux": 4}));
+    });
+
+    test("the second map's values win by default", () {
+      expect(mergeMaps({"foo": 1, "bar": 2}, {"bar": 3, "baz": 4}),
+          equals({"foo": 1, "bar": 3, "baz": 4}));
+    });
+
+    test("uses the callback to merge values", () {
+      expect(mergeMaps({"foo": 1, "bar": 2}, {"bar": 3, "baz": 4},
+              value: (value1, value2) => value1 + value2),
+          equals({"foo": 1, "bar": 5, "baz": 4}));
+    });
+  });
+
+  group("groupBy()", () {
+    test("returns an empty map for an empty iterable", () {
+      expect(groupBy([], expectAsync((_) {}, count: 0)), isEmpty);
+    });
+
+    test("groups elements by the function's return value", () {
+      expect(
+          groupBy(["foo", "bar", "baz", "bop", "qux"], (string) => string[1]),
+          equals({"o": ["foo", "bop"], "a": ["bar", "baz"], "u": ["qux"]}));
+    });
+  });
+
+  group("minBy()", () {
+    test("returns null for an empty iterable", () {
+      expect(
+          minBy([], expectAsync((_) {}, count: 0),
+              compare: expectAsync((_, __) {}, count: 0)),
+          isNull);
+    });
+
+    test("returns the element for which the ordering function returns the "
+        "smallest value", () {
+      expect(
+          minBy(
+              [{"foo": 3}, {"foo": 5}, {"foo": 4}, {"foo": 1}, {"foo": 2}],
+              (map) => map["foo"]),
+          equals({"foo": 1}));
+    });
+
+    test("uses a custom comparator if provided", () {
+      expect(
+          minBy(
+              [{"foo": 3}, {"foo": 5}, {"foo": 4}, {"foo": 1}, {"foo": 2}],
+              (map) => map,
+              compare: (map1, map2) => map1["foo"].compareTo(map2["foo"])),
+          equals({"foo": 1}));
+    });
+  });
+
+  group("maxBy()", () {
+    test("returns null for an empty iterable", () {
+      expect(
+          maxBy([], expectAsync((_) {}, count: 0),
+              compare: expectAsync((_, __) {}, count: 0)),
+          isNull);
+    });
+
+    test("returns the element for which the ordering function returns the "
+        "largest value", () {
+      expect(
+          maxBy(
+              [{"foo": 3}, {"foo": 5}, {"foo": 4}, {"foo": 1}, {"foo": 2}],
+              (map) => map["foo"]),
+          equals({"foo": 5}));
+    });
+
+    test("uses a custom comparator if provided", () {
+      expect(
+          maxBy(
+              [{"foo": 3}, {"foo": 5}, {"foo": 4}, {"foo": 1}, {"foo": 2}],
+              (map) => map,
+              compare: (map1, map2) => map1["foo"].compareTo(map2["foo"])),
+          equals({"foo": 5}));
+    });
+  });
+
+  group("transitiveClosure()", () {
+    test("returns an empty map for an empty graph", () {
+      expect(transitiveClosure({}), isEmpty);
+    });
+
+    test("returns the input when there are no transitive connections", () {
+      expect(transitiveClosure({
+        "foo": ["bar"],
+        "bar": [],
+        "bang": ["qux", "zap"],
+        "qux": [],
+        "zap": []
+      }), equals({
+        "foo": ["bar"],
+        "bar": [],
+        "bang": ["qux", "zap"],
+        "qux": [],
+        "zap": []
+      }));
+    });
+
+    test("flattens transitive connections", () {
+      expect(transitiveClosure({
+        "qux": [],
+        "bar": ["baz"],
+        "baz": ["qux"],
+        "foo": ["bar"]
+      }), equals({
+        "foo": ["bar", "baz", "qux"],
+        "bar": ["baz", "qux"],
+        "baz": ["qux"],
+        "qux": []
+      }));
+    });
+
+    test("handles loops", () {
+      expect(transitiveClosure({
+        "foo": ["bar"],
+        "bar": ["baz"],
+        "baz": ["foo"]
+      }), equals({
+        "foo": ["bar", "baz", "foo"],
+        "bar": ["baz", "foo", "bar"],
+        "baz": ["foo", "bar", "baz"]
+      }));
+    });
+  });
+}