Add set operations. Union, intersect and difference

README.md

@@ -10,6 +10,9 @@
 ## Contents
 
 * [Anagrams of string (with duplicates)](#anagrams-of-string-with-duplicates)
+* [Array difference](#array-difference)
+* [Array intersection](#array-intersection)
+* [Array union](#array-union)
 * [Average of array of numbers](#average-of-array-of-numbers)
 * [Bottom visible](#bottom-visible)
 * [Capitalize first letter of every word](#capitalize-first-letter-of-every-word)
@@ -21,7 +24,6 @@
 * [Current URL](#current-url)
 * [Curry](#curry)
 * [Deep flatten array](#deep-flatten-array)
-* [Difference between arrays](#difference-between-arrays)
 * [Distance between two points](#distance-between-two-points)
 * [Divisible by number](#divisible-by-number)
 * [Escape regular expression](#escape-regular-expression)
@@ -85,6 +87,33 @@ const anagrams = str => {
 // anagrams('abc') -> ['abc','acb','bac','bca','cab','cba']
 ```
 
+### Array difference (complement)
+
+Create a `Set` from `b`, then use `Array.filter()` on `a` to only keep values not contained in `b`.
+
+```js
+const difference = (a, b) => { const s = new Set(b); return a.filter(x => !s.has(x)); }
+// difference([1,2,3], [1,2]) -> [3]
+```
+
+### Array intersection (Common values between two arrays)
+
+Create a `Set` from `b`, then use `Array.filter()` on `a` to only keep values contained in `b`.
+
+```js
+const intersection = (a, b) => { const s = new Set(b); return a.filter(x => s.has(x)); }
+// intersection([1,2,3], [4,3,2]) -> [2,3]
+```
+
+### Array union
+
+Create a `Set` with all values of `a` and `b` and convert to an array.
+
+```js
+const union = (a, b) => Array.from(new Set([...a, ...b]))
+// union([1,2,3], [4,3,2]) -> [1,2,3,4]
+```
+
 ### Average of array of numbers
 
 Use `Array.reduce()` to add each value to an accumulator, initialized with a value of `0`, divide by the `length` of the array.
@@ -211,15 +240,6 @@ const deepFlatten = arr =>
 // deepFlatten([1,[2],[[3],4],5]) -> [1,2,3,4,5]
 ```
 
-### Difference between arrays
-
-Use `filter()` to remove values that are part of `values`, determined using `includes()`.
-
-```js
-const difference = (arr, values) => arr.filter(v => !values.includes(v));
-// difference([1,2,3], [1,2]) -> [3]
-```
-
 ### Distance between two points
 
 Use `Math.hypot()` to calculate the Euclidean distance between two points.

snippets/array-difference.md

@@ -0,0 +1,8 @@
+### Array difference (complement)
+
+Create a `Set` from `b`, then use `Array.filter()` on `a` to only keep values not contained in `b`.
+
+```js
+const difference = (a, b) => { const s = new Set(b); return a.filter(x => !s.has(x)); }
+// difference([1,2,3], [1,2]) -> [3]
+```

snippets/array-intersection.md

@@ -0,0 +1,8 @@
+### Array intersection (Common values between two arrays)
+
+Create a `Set` from `b`, then use `Array.filter()` on `a` to only keep values contained in `b`.
+
+```js
+const intersection = (a, b) => { const s = new Set(b); return a.filter(x => s.has(x)); }
+// intersection([1,2,3], [4,3,2]) -> [2,3]
+```

snippets/array-union.md

@@ -0,0 +1,8 @@
+### Array union
+
+Create a `Set` with all values of `a` and `b` and convert to an array.
+
+```js
+const union = (a, b) => Array.from(new Set([...a, ...b]))
+// union([1,2,3], [4,3,2]) -> [1,2,3,4]
+```

snippets/difference-between-arrays.md

@@ -1,8 +0,0 @@
-### Difference between arrays
-
-Use `filter()` to remove values that are part of `values`, determined using `includes()`.
-
-```js
-const difference = (arr, values) => arr.filter(v => !values.includes(v));
-// difference([1,2,3], [1,2]) -> [3]
-```