Merge branch 'master' into master

snippets/array-concatenation.md

@@ -1,6 +1,6 @@
 ### Array concatenation
 
-Use `Array.concat()` to concatenate and array with any additional arrays and/or values, specified in `args`.
+Use `Array.concat()` to concatenate an array with any additional arrays and/or values, specified in `args`.
 
 ```js
 const arrayConcat = (arr, ...args) => arr.concat(...args);

snippets/array-difference.md

@@ -3,6 +3,6 @@
 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)); }
+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

@@ -3,6 +3,6 @@
 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)); }
+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

@@ -3,6 +3,6 @@
 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]))
+const union = (a, b) => Array.from(new Set([...a, ...b]));
 // union([1,2,3], [4,3,2]) -> [1,2,3,4]
 ```

snippets/collatz-algorithm.md

@@ -0,0 +1,9 @@
+### Collatz algorithm
+
+If `n` is even, return `n/2`. Otherwise  return `3n+1`.
+
+```js
+const collatz = n => (n % 2 == 0) ? (n / 2) : (3 * n + 1);
+// collatz(8) --> 4
+// collatz(5) --> 16
+```

snippets/curry.md

@@ -6,13 +6,10 @@ Otherwise return a curried function `f` that expects the rest of the arguments.
 If you want to curry a function that accepts a variable number of arguments (a variadic function, e.g. `Math.min()`), you can optionally pass the number of arguments to the second parameter `arity`.
 
 ```js
-const curry = (f, arity = f.length, next) =>
-  (next = prevArgs =>
-    nextArg => {
-      const args = [ ...prevArgs, nextArg ];
-      return args.length >= arity ? f(...args) : next(args);
-    }
-  )([]);
+const curry = (fn, arity = fn.length, ...args) =>
+  arity <= args.length
+    ? fn(...args)
+    : curry.bind(null, fn, arity, ...args)
 // curry(Math.pow)(2)(10) -> 1024
 // curry(Math.min, 3)(10)(50)(2) -> 2
 ```

snippets/drop-elements-in-array.md

@@ -4,9 +4,9 @@ Loop through the array, using `Array.shift()` to drop the first element of the a
 Returns the remaining elements.
 
 ```js
-const dropElements = (arr,func) => {
-  while(arr.length > 0 && !func(arr[0])) arr.shift();
+const dropElements = (arr, func) => {
+  while (arr.length > 0 && !func(arr[0])) arr.shift();
   return arr;
-}
+};
 // dropElements([1, 2, 3, 4], n => n >= 3) -> [3,4]
 ```

snippets/element-is-visible-in-viewport.md

@@ -12,7 +12,7 @@ const elementIsVisibleInViewport = (el, partiallyVisible = false) => {
     ? ((top > 0 && top < innerHeight) || (bottom > 0 && bottom < innerHeight)) &&
       ((left > 0 && left < innerWidth) || (right > 0 && right < innerWidth))
     : top >= 0 && left >= 0 && bottom <= innerHeight && right <= innerWidth;
-}
+};
 // e.g. 100x100 viewport and a 10x10px element at position {top: -1, left: 0, bottom: 9, right: 10}
 // elementIsVisibleInViewport(el) -> false (not fully visible)
 // elementIsVisibleInViewport(el, true) -> true (partially visible)

snippets/fill-array.md

@@ -0,0 +1,10 @@
+### Fill array
+
+Use `Array.map()` to map values between `start` (inclusive) and `end` (exclusive) to `value`.
+Omit `start` to start at the first element and/or `end` to finish at the last.
+
+```js
+const fillArray = (arr, value, start = 0, end = arr.length) =>
+  arr.map((v, i) => i >= start && i < end ? value : v);
+// fillArray([1,2,3,4],'8',1,3) -> [1,'8','8',4]
+```

snippets/flatten-array-up-to-depth.md

@@ -0,0 +1,13 @@
+### Flatten array up to depth
+
+Use recursion, decrementing `depth` by 1 for each level of depth.
+Use `Array.reduce()` and `Array.concat()` to merge elements or arrays.
+Base case, for `depth` equal to `1` stops recursion.
+Omit the second element, `depth` to flatten only to a depth of `1` (single flatten).
+
+```js
+const flattenDepth = (arr, depth = 1) =>
+  depth != 1 ? arr.reduce((a, v) => a.concat(Array.isArray(v) ? flattenDepth(v, depth - 1) : v), [])
+  : arr.reduce((a, v) => a.concat(v), []);
+// flattenDepth([1,[2],[[[3],4],5]], 2) -> [1,2,[3],4,5]
+```

snippets/group-by.md

@@ -5,10 +5,8 @@ Use `Array.reduce()` to create an object, where the keys are produced from the m
 
 ```js
 const groupBy = (arr, func) =>
-  (typeof func === 'function' ? arr.map(func) : arr.map(val => val[func]))
-    .reduce((acc, val, i) => {
-      acc[val] = acc[val] === undefined ? [arr[i]] : acc[val].concat(arr[i]); return acc;
-    }, {});
+  arr.map(typeof func === 'function' ? func : val => val[func])
+    .reduce((acc, val, i) => { acc[val] = (acc[val] || []).concat(arr[i]); return acc; }, {});
 // groupBy([6.1, 4.2, 6.3], Math.floor) -> {4: [4.2], 6: [6.1, 6.3]}
 // groupBy(['one', 'two', 'three'], 'length') -> {3: ['one', 'two'], 5: ['three']}
 ```

snippets/is-array.md

@@ -3,7 +3,7 @@
 Use `Array.isArray()` to check if a value is classified as an array.
 
 ```js
-const isArray = val => val && Array.isArray(val);
+const isArray = val => !!val && Array.isArray(val);
 // isArray(null) -> false
 // isArray([1]) -> true
 ```

snippets/ordinal-suffix-of-number.md

@@ -7,9 +7,9 @@ If digit is found in teens pattern, use teens ordinal.
 ```js
 const toOrdinalSuffix = num => {
   const int = parseInt(num), digits = [(int % 10), (int % 100)],
-    ordinals = ["st", "nd", "rd", "th"], oPattern = [1,2,3,4],
-    tPattern = [11, 12, 13, 14, 15, 16, 17, 18, 19]
-  return oPattern.includes(digits[0]) && !tPattern.includes(digits[1]) ? int + ordinals[digits[0]-1] : int + ordinals[3];
-}
+    ordinals = ['st', 'nd', 'rd', 'th'], oPattern = [1, 2, 3, 4],
+    tPattern = [11, 12, 13, 14, 15, 16, 17, 18, 19];
+  return oPattern.includes(digits[0]) && !tPattern.includes(digits[1]) ? int + ordinals[digits[0] - 1] : int + ordinals[3];
+};
 // toOrdinalSuffix("123") -> "123rd"
 ```

snippets/standard-deviation.md

@@ -11,7 +11,7 @@ const standardDeviation = (arr, usePopulation = false) => {
     arr.reduce((acc, val) => acc.concat(Math.pow(val - mean, 2)), [])
        .reduce((acc, val) => acc + val, 0) / (arr.length - (usePopulation ? 0 : 1))
   );
- }
+};
 // standardDeviation([10,2,38,23,38,23,21]) -> 13.284434142114991 (sample)
 // standardDeviation([10,2,38,23,38,23,21], true) -> 12.29899614287479 (population)
 ```

snippets/take.md

@@ -4,7 +4,6 @@ Use `Array.slice()` to create a slice of the array with `n` elements taken from
 
 ```js
 const take = (arr, n = 1) => arr.slice(0, n);
-
 // take([1, 2, 3], 5) -> [1, 2, 3]
 // take([1, 2, 3], 0) -> []
 ```