lodash remove duplicated

snippets/URL-parameters.md

@@ -5,7 +5,7 @@ Pass `location.search` as the argument to apply to the current `url`.
 
 ```js
 const getUrlParameters = url =>
-  url.match(/([^?=&]+)(=([^&]*))?/g).reduce(
+  url.match(/([^?=&]+)(=([^&]*))/g).reduce(
     (a, v) => (a[v.slice(0, v.indexOf('='))] = v.slice(v.indexOf('=') + 1), a), {}
   );
 // getUrlParameters('http://url.com/page?name=Adam&surname=Smith') -> {name: 'Adam', surname: 'Smith'}

snippets/array-concatenation.md

@@ -0,0 +1,8 @@
+### Array concatenation
+
+Use `Array.concat()` to concatenate and array with any additional arrays and/or values, specified in `args`.
+
+```js
+const ArrayConcat = (arr, ...args) => arr.concat(...args); 
+// ArrayConcat([1], [1, 2, 3, [4]]) -> [1, 2, 3, [4]]
+```

snippets/array-difference.md

@@ -1,4 +1,4 @@
-### Array difference (complement)
+### Array difference
 
 Create a `Set` from `b`, then use `Array.filter()` on `a` to only keep values not contained in `b`.
 

snippets/array-intersection.md

@@ -1,4 +1,4 @@
-### Array intersection (Common values between two arrays)
+### Array intersection
 
 Create a `Set` from `b`, then use `Array.filter()` on `a` to only keep values contained in `b`.
 

snippets/chunk-array.md

@@ -1,11 +1,11 @@
 ### Chunk array
 
-Use `Array.apply()` to create a new array, that fits the number of chunks that will be produced.
-Use `Array.map()` to map each element of the new array to a chunk the length of `size`.
+Use `Array.from()` to create a new array, that fits the number of chunks that will be produced.
+Use `Array.slice()` to map each element of the new array to a chunk the length of `size`.
 If the original array can't be split evenly, the final chunk will contain the remaining elements.
 
 ```js
 const chunk = (arr, size) =>
-  Array.apply(null, {length: Math.ceil(arr.length / size)}).map((v, i) => arr.slice(i * size, i * size + size));
+  Array.from({length: Math.ceil(arr.length / size)}, (v, i) => arr.slice(i * size, i * size + size));
 // chunk([1,2,3,4,5], 2) -> [[1,2],[3,4],5]
 ```

snippets/concat.md

@@ -1,8 +0,0 @@
-### Concat
-
-Creates a new array concatenating array with any additional arrays and/or values `args` using `Array.concat()`.
-
-```js
-const ArrayConcat = (arr, ...args) => arr.concat(...args); 
-// ArrayConcat([1], [1, 2, 3, [4]]) -> [1, 2, 3, [4]]
-```

snippets/group-by.md

@@ -0,0 +1,14 @@
+### Group by
+
+Use `Array.map()` to map the values of an array to a function or property name.
+Use `Array.reduce()` to create an object, where the keys are produced from the mapped results.
+
+```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;
+    }, {});
+// 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/head-of-list.md

@@ -1,6 +1,6 @@
 ### Head of list
 
-Return `arr[0]`.
+Use `arr[0]` to return the first element of the passed array.
 
 ```js
 const head = arr => arr[0];

snippets/initial-of-list.md

@@ -1,6 +1,6 @@
 ### Initial of list
 
-Return `arr.slice(0,-1)`.
+Use `arr.slice(0,-1)`to return all but the last element of the array.
 
 ```js
 const initial = arr => arr.slice(0, -1);

snippets/last-of-list.md

@@ -1,6 +1,6 @@
 ### Last of list
 
-Return `arr.slice(-1)[0]`.
+Use `arr.slice(-1)[0]` to get the last element of the given array.
 
 ```js
 const last = arr => arr.slice(-1)[0];

snippets/randomize-order-of-array.md

@@ -1,8 +0,0 @@
-### Randomize order of array
-
-Use `Array.sort()` to reorder elements, utilizing `Math.random()` to randomize the sorting.
-
-```js
-const randomizeOrder = arr => arr.sort((a, b) => Math.random() >= 0.5 ? -1 : 1);
-// randomizeOrder([1,2,3]) -> [1,3,2]
-```

snippets/shuffle-array-values.md

@@ -1,12 +0,0 @@
-### Shuffle array values
-
-Create an array of random values by using `Array.map()` and `Math.random()`.
-Use `Array.sort()` to sort the elements of the original array based on the random values.
-
-```js
-const shuffle = arr => {
-  let r = arr.map(Math.random);
-  return arr.sort((a, b) => r[a] - r[b]);
-};
-// shuffle([1,2,3]) -> [2, 1, 3]
-```

snippets/shuffle-array.md

@@ -0,0 +1,8 @@
+### Shuffle array
+
+Use `Array.sort()` to reorder elements, using `Math.random()` in the comparator.
+
+```js
+const shuffle = arr => arr.sort(() => Math.random() - 0.5);
+// shuffle([1,2,3]) -> [2,3,1]
+```

snippets/sleep.md

@@ -0,0 +1,14 @@
+### Sleep
+
+Delay executing part of an `async` function, by putting it to sleep, returning a `Promise`.
+
+```js
+const sleep = ms => new Promise(resolve => setTimeout(resolve, ms));
+/*
+async function sleepyWork() {
+  console.log('I\'m going to sleep for 1 second.');
+  await sleep(1000);
+  console.log('I woke up after 1 second.');
+}
+*/
+```

snippets/standard-deviation.md

@@ -0,0 +1,17 @@
+### Standard deviation
+
+Use `Array.reduce()` to calculate the mean, variance and the sum of the variance of the values, the variance of the values, then
+determine the standard deviation.
+You can omit the second argument to get the sample standard deviation or set it to `true` to get the population standard deviation.
+
+```js
+const standardDeviation = (arr, usePopulation = false) => {
+  const mean = arr.reduce((acc, val) => acc + val, 0) / arr.length;
+  return Math.sqrt(
+    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

@@ -0,0 +1,10 @@
+### Take
+
+Use `Array.slice()` to create a slice of the array with `n` elements taken from the beginning.
+
+```js
+const take = (arr, n = 1) => arr.slice(0, n);
+
+// take([1, 2, 3], 5) -> [1, 2, 3]
+// take([1, 2, 3], 0) -> []
+```

snippets/validate-email.md

@@ -0,0 +1,10 @@
+### Validate email
+
+Use a regular experssion to check if the email is valid.
+Returns `true` if email is valid, `false` if not.
+
+```js
+const validateEmail = str =>
+  /^(([^<>()\[\]\\.,;:\s@"]+(\.[^<>()\[\]\\.,;:\s@"]+)*)|(".+"))@((\[[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\])|(([a-zA-Z\-0-9]+\.)+[a-zA-Z]{2,}))$/.test(str);
+// validateEmail(mymail@gmail.com) -> true
+```