Map, filter, reduce

chapter02/src/map_filter_reduce.js

@@ -0,0 +1,37 @@
+/* @flow */
+/* eslint-disable no-unused-vars, one-var */
+
+const someArray: Array<number> = [22, 9, 60, 12, 4, 56];
+const totalSum = someArray.reduce(
+    (acc: number, val: number) => acc + val,
+    0
+); // 163
+
+const names = ["Juan", "María", "Sylvia", "Federico"];
+const bulletedList =
+    "<ul>" +
+    names.reduce((acc, val) => `${acc}<li>${val}</li>`, "") +
+    "</ul>";
+// <ul><li>Juan</li><li>María</li><li>Sylvia</li><li>Federico</li></ul>
+
+type person = { name: string, sex: string, age: number };
+const family: Array<person> = [
+    { name: "Huey", sex: "M", age: 7 },
+    { name: "Dewey", sex: "M", age: 8 },
+    { name: "Louie", sex: "M", age: 9 },
+    { name: "Daisy", sex: "F", age: 25 },
+    { name: "Donald", sex: "M", age: 30 },
+    { name: "Della", sex: "F", age: 30 }
+];
+
+const ages = family.map(x => x.age);
+// [7, 8, 9, 25, 30, 30]
+
+const males = family.filter(x => x.sex === "M");
+console.log(males.length); // 4
+
+const eldestMaleAge = family
+    .filter(x => x.sex === "M")
+    .map(x => x.age)
+    .reduce((acc, val) => Math.max(acc, val), 0);
+console.log(eldestMaleAge); // 30