upsert function and accompanying tests

src/index.js

@@ -187,6 +187,7 @@ export { default as spreadPath } from './spreadPath';
 export { default as flattenProp } from './flattenProp';
 export { default as flattenPath } from './flattenPath';
 export { default as unzipObjWith } from './unzipObjWith';
+export { default as upsert } from './upsert';
 export { default as zipObjWith } from './zipObjWith';
 export { default as isPrototypeOf } from './isPrototypeOf';
 // Relation

src/upsert.js

@@ -0,0 +1,56 @@
+import { curry, cond, equals } from 'ramda';
+
+/**
+ * Adds a value to a map if the map does not already have something at key otherwise updates an existing value at key.
+ *
+ * @func upsert
+ * @memberOf RA
+ * @category Object
+ * @since
+ * @sig  k -> (() -> String) -> (() -> String) -> [k, v]
+ * @param {string} key The key at which to update or insert the value
+ * @param {Function} update The function to generate the value if key exists
+ * @param {Function} insert The function to generate the value if key does not exist
+ * @param {(Array|Object|Map)} collection The collection into which the value is inserted or updated
+ * @return {(Array|Object|Map)} The collection into which the value has been inserted or updated
+ * @see
+ * @example
+ *
+ * RA.upsert('key', () => 'new value', () => 'initial value', {});
+ * //=> {key: 'initial value'}
+ */
+
+ const emplace = curry((_, key, update, insert, collection) => {
+   if (collection[key]) {
+     collection[key] = update();
+   } else {
+     collection[key] = insert();
+   }
+   return collection;
+ })
+
+ const emplaceMap = curry((_, key, update, insert, collection) => {
+   if (collection.get(key)) {
+     collection.set(key, update());
+   } else {
+     collection.set(key, insert());
+   }
+   return collection;
+ })
+
+ const polymorphicDispatch = cond([
+   [equals("[object Array]"),   emplace],
+   [equals("[object Object]"),   emplace],
+   [equals("[object Map]"),   emplaceMap],
+ ]);
+
+ const upsert = curry((key, update, insert, collection) =>
+     polymorphicDispatch(Object.prototype.toString.call(collection))(
+         key,
+         update,
+         insert,
+         collection
+     )
+ );
+
+export default upsert;

test/upsert.js

@@ -0,0 +1,19 @@
+import { assert } from 'chai';
+
+import * as RA from '../src';
+
+describe('upsert', function () {
+  console.log(RA.upsert)
+  it('should work on objects', function () {
+    assert.deepEqual(RA.upsert('key', () => 'new value', () => 'initial value', {}), {key: 'initial value'});
+    assert.deepEqual(RA.upsert('key', () => 'new value', () => 'initial value', {key: 'value'}), {key: 'new value'});
+  });
+  it('should work on arrays', function () {
+    assert.deepEqual(RA.upsert(1, () => 'new value', () => 'initial value', []), [, 'initial value']);
+    assert.deepEqual(RA.upsert(1, () => 'new value', () => 'initial value', ['first value', 'second vaue']), ['first value', 'new value']);
+  });
+  it('should work on maps', function () {
+    assert.deepEqual(RA.upsert('key', () => 'new value', () => 'initial value', new Map()), new Map([['key', 'initial value']]));
+    assert.deepEqual(RA.upsert('key', () => 'new value', () => 'initial value', new Map([['key', 'initial value']])), new Map([['key', 'new value']]));
+  });
+});