Add merge()

Author: winterbe

src/Sequence.ts

@@ -68,6 +68,7 @@ import minWith from "./minWith";
 import dropWhile from "./dropWhile";
 import takeWhile from "./takeWhile";
 import asIterable from "./asIterable";
+import merge from "./merge";
 
 /**
  * A Sequence accepts an iterator and provides a fluent functional API consisting
@@ -152,6 +153,7 @@ export default class Sequence<T> {
     minBy = minBy;
     minWith = minWith;
     asIterable = asIterable;
+    merge = merge;
 }
 
 export function sequenceOf<T>(...args: Array<T>): Sequence<T> {

src/merge.ts

@@ -0,0 +1,37 @@
+import Sequence, {asSequence} from "./Sequence";
+
+/**
+ * Merges the elements of both sequences into a new sequence. Each element of this sequence is eventually replaced with
+ * an element of the other sequence by comparing results of the given `selector` function. If no value is found in the other
+ * sequence the element is retained. New elements of the other sequence are appended to the end of the new sequence or
+ * prepended to the start of the new sequence, if `prependNewValues` is set to `true`.
+ *
+ * @param {Sequence<T>} other
+ * @param {(value: T) => S} selector
+ * @param prependNewValues
+ * @returns {Sequence<T>}
+ */
+function merge<T, S>(this: Sequence<T>, other: Sequence<T> | Iterable<T>, selector: (value: T) => S, prependNewValues: boolean = false): Sequence<T> {
+    let mergeValues = other instanceof Sequence
+        ? other.toArray()
+        : asSequence(other).toArray();
+    const leftValues = this.toArray();
+    const result = leftValues.map(left => {
+        const selected = selector(left);
+        const right = asSequence(mergeValues)
+            .find(it => selector(it) === selected);
+        if (right != null) {
+            mergeValues = mergeValues.filter(it => it !== right);
+            return right;
+        } else {
+            return left;
+        }
+    });
+    if (prependNewValues) {
+        return asSequence([...mergeValues, ...result]);
+    } else {
+        return asSequence([...result, ...mergeValues]);
+    }
+}
+
+export default merge;

test/merge.test.ts

@@ -0,0 +1,31 @@
+import {sequenceOf} from "../src/Sequence";
+
+describe("merge", () => {
+    it("should merge both sequences", () => {
+        const result = sequenceOf({id: 1, val: "a"}, {id: 2, val: "b"}, {id: 3, val: "c"})
+            .merge(sequenceOf({id: 2, val: "bb"}), it => it.id)
+            .toArray();
+        expect(result).toEqual([{id: 1, val: "a"}, {id: 2, val: "bb"}, {id: 3, val: "c"}]);
+    });
+
+    it("should merge given array", () => {
+        const result = sequenceOf({id: 1, val: "a"}, {id: 2, val: "b"}, {id: 3, val: "c"})
+            .merge([{id: 2, val: "bb"}], it => it.id)
+            .toArray();
+        expect(result).toEqual([{id: 1, val: "a"}, {id: 2, val: "bb"}, {id: 3, val: "c"}]);
+    });
+
+    it("should merge both sequences and append new values", () => {
+        const result = sequenceOf({id: 1, val: "a"}, {id: 2, val: "b"}, {id: 3, val: "c"})
+            .merge(sequenceOf({id: 2, val: "bb"}, {id: 4, val: "d"}), it => it.id)
+            .toArray();
+        expect(result).toEqual([{id: 1, val: "a"}, {id: 2, val: "bb"}, {id: 3, val: "c"}, {id: 4, val: "d"}]);
+    });
+
+    it("should merge both sequences and prepend new values", () => {
+        const result = sequenceOf({id: 1, val: "a"}, {id: 2, val: "b"}, {id: 3, val: "c"})
+            .merge(sequenceOf({id: 2, val: "bb"}, {id: 4, val: "d"}), it => it.id, true)
+            .toArray();
+        expect(result).toEqual([{id: 4, val: "d"}, {id: 1, val: "a"}, {id: 2, val: "bb"}, {id: 3, val: "c"}]);
+    });
+});