feat: Add functions sum() and avg() to DataArray (#2351)

docs/docs/api/data-array.md

@@ -116,6 +116,12 @@ export interface DataArray<T> {
     /** Run a lambda on each element in the array. */
     forEach(f: ArrayFunc<T, void>): void;
 
+    /** Calculate the sum of the elements of the array. */
+    sum(): number;
+
+    /** Calculate the average of the elements of the array. */
+    avg(): number | undefined;
+
     /** Convert this to a plain javascript array. */
     array(): T[];
 

src/api/data-array.ts

@@ -115,6 +115,12 @@ export interface DataArray<T> {
     /** Run a lambda on each element in the array. */
     forEach(f: ArrayFunc<T, void>): void;
 
+    /** Calculate the sum of the elements of the array. */
+    sum(): number;
+
+    /** Calculate the average of the elements of the array. */
+    avg(): number | undefined;
+
     /** Convert this to a plain javascript array. */
     array(): T[];
 
@@ -164,6 +170,8 @@ class DataArrayImpl<T> implements DataArray<T> {
         "defaultComparator",
         "toString",
         "settings",
+        "sum",
+        "avg"
     ]);
 
     private static ARRAY_PROXY: ProxyHandler<DataArrayImpl<any>> = {
@@ -446,6 +454,14 @@ class DataArrayImpl<T> implements DataArray<T> {
         }
     }
 
+    public sum() {
+        return this.values.reduce((a, b) => a + b, 0);
+    }
+
+    public avg() {
+        return this.sum() / this.values.length;
+    }
+
     public array(): T[] {
         return ([] as any[]).concat(this.values);
     }

src/test/api/data-array.test.ts

@@ -179,6 +179,16 @@ describe("last", () => {
     test("nonempty", () => expect(da([1, 2, 3]).last()).toEqual(3));
 });
 
+describe("sum", () => {
+    test("empty", () => expect(da([]).sum()).toEqual(0));
+    test("numbers", () => expect(da([1, 10, 2]).sum()).toEqual(13));
+});
+
+describe("avg", () => {
+    test("empty", () => expect(da([]).avg()).toEqual(NaN));
+    test("numbers", () => expect(da([5, 10, 15]).avg()).toEqual(10));
+});
+
 /** Utility function for quickly creating a data array. */
 function da<T>(val: T[]): DataArray<T> {
     return DataArray.wrap(val, DEFAULT_QUERY_SETTINGS);