Rename js snippets

snippets/js/s/function-based-array-unique-values.md

@@ -0,0 +1,34 @@
+---
+title: Unique values in array based on function
+type: snippet
+language: javascript
+tags: [array]
+cover: sunrise-over-mountains
+dateModified: 2021-10-13T19:29:39+02:00
+---
+
+Finds all unique values of an array, based on a provided comparator function.
+
+- Use `Array.prototype.reduce()` and `Array.prototype.some()` to create an array containing only the first unique occurrence of each value, based on the comparator function, `fn`.
+- The comparator function takes two arguments: the values of the two elements being compared.
+
+```js
+const uniqueElementsBy = (arr, fn) =>
+  arr.reduce((acc, v) => {
+    if (!acc.some(x => fn(v, x))) acc.push(v);
+    return acc;
+  }, []);
+```
+
+```js
+uniqueElementsBy(
+  [
+    { id: 0, value: 'a' },
+    { id: 1, value: 'b' },
+    { id: 2, value: 'c' },
+    { id: 1, value: 'd' },
+    { id: 0, value: 'e' }
+  ],
+  (a, b) => a.id == b.id
+); // [ { id: 0, value: 'a' }, { id: 1, value: 'b' }, { id: 2, value: 'c' } ]
+```