From 03ee6f73ca30fabd4f12819df7aea14a0ada3151 Mon Sep 17 00:00:00 2001
From: Angelos Chalaris <chalarangelo@gmail.com>
Date: Wed, 18 Jul 2018 20:49:07 +0300
Subject: [PATCH] add uniqueElements By and ByRight

---
 snippets/filterNonUniqueBy.md     |  4 ++--
 snippets/uniqueElementsBy.md      | 27 +++++++++++++++++++++++++++
 snippets/uniqueElementsByRight.md | 27 +++++++++++++++++++++++++++
 3 files changed, 56 insertions(+), 2 deletions(-)
 create mode 100644 snippets/uniqueElementsBy.md
 create mode 100644 snippets/uniqueElementsByRight.md

diff --git a/snippets/filterNonUniqueBy.md b/snippets/filterNonUniqueBy.md
index 4fa5a11c0..a2abdfe6a 100644
--- a/snippets/filterNonUniqueBy.md
+++ b/snippets/filterNonUniqueBy.md
@@ -19,6 +19,6 @@ filterNonUniqueBy(
 		{ id: 1, value: 'd' },
 		{ id: 0, value: 'e' },
 	],
-	(a, b) => a.id != b.id
-); // [{id: 2, value: 'c'}]
+	(a, b) => a.id == b.id
+); // [ { id: 2, value: 'c' } ]
 ```
diff --git a/snippets/uniqueElementsBy.md b/snippets/uniqueElementsBy.md
new file mode 100644
index 000000000..08bf7b19a
--- /dev/null
+++ b/snippets/uniqueElementsBy.md
@@ -0,0 +1,27 @@
+### uniqueElementsBy
+
+Returns all unique values of an array, based on a provided comparator function.
+
+Use `Array.reduce()` and `Array.some()` for an array containing only the first unique occurence 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' } ]
+```
diff --git a/snippets/uniqueElementsByRight.md b/snippets/uniqueElementsByRight.md
new file mode 100644
index 000000000..42b351438
--- /dev/null
+++ b/snippets/uniqueElementsByRight.md
@@ -0,0 +1,27 @@
+### uniqueElementsByRight
+
+Returns all unique values of an array, based on a provided comparator function.
+
+Use `Array.reduce()` and `Array.some()` for an array containing only the last unique occurence 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 uniqueElementsByRight = (arr, fn) =>
+	arr.reduce((acc, v) => {
+		if (!acc.some(x => fn(v, x))) acc.push(v);
+		return acc;
+	}, []);
+```
+
+```js
+uniqueElementsByRight(
+	[
+		{ 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: 'e' }, { id: 1, value: 'd' }, { id: 2, value: 'c' } ]
+```