javascript convert elements of an array into array for themselves - javascript

How can I convert the elements of the array into another array?
let a = [2, 4, 0, 8, 9, 15]
and the result will be :
a = [[2], [4], [0], [8], [9], [15]]


Use Array#map to iterate the array, and wrap each item in an array:
let a = [2, 4, 0, 8, 9, 15]
const result = a.map((n) => [n])
console.log(JSON.stringify(result))


let a = [2, 4, 0, 8, 9, 15];
let b = a.map((item) => [item]);


a = [2, 4, 0, 8, 9, 15]
console.log(result = a.map((n) => [n]))
b=[]
//you can try below also
for (i in a){
b.push([i]);
}

Related

Splitting an array into 3 unequal arrays in JavaScript

Suppose I have an array of
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15]
And I want to split it in 3, with two arrays containing the first and last X elements of the original array, and the third array containing the remaining elements, like so:
#1 - [0, 1, 2]
#2 - [3, 4, 5, 6, 7, 8, 9, 10, 11, 12]
#3 - [13, 14, 15]
Is there a shorter/better way of doing that instead of:
const splitBy = 3;
const originalArray = Array.from(Array(16).keys());
const result = [
originalArray.slice(0, splitBy),
originalArray.slice(splitBy, -splitBy),
originalArray.slice(-splitBy),
];
console.log(result)

"better" is subjective... however, if you need this more than once, a generic function could be an option:
function multiSlice(a, ...slices) {
let res = [], i = 0
for (let s of slices) {
res.push(a.slice(i, s))
i = s
}
res.push(a.slice(i))
return res
}
// for example,
const originalArray = Array.from(Array(16).keys());
console.log(multiSlice(originalArray, 3, -3))
console.log(multiSlice(originalArray, 2, 5, 10, 12))

Shuffle nested arrays in Javascript

I'm trying to sort multiple arrays within an array (which also has to be shuffled). A simplified example is:
let toShuffle = [
[1, 2, 3, 4, 5],
[9, 8, 7, 6, 5],
[10, 67, 19 ,27]
...
];
const shuffled = shuffle(toShuffle);
// outout would look something like:
// [
// [8, 6, 5, 7, 9],
// [4, 3, 1, 5, 2],
// [19, 26, 10, 67],
// ...
// ]
This needs to be flexible, so any number of arrays with any amount of values should be valid.
Here is what I've tried:
function shuffle(a) {
for (let e in a) {
if (Array.isArray(a[e])) {
a[e] = shuffle(a[e]);
} else {
a.splice(e, 1);
a.splice(Math.floor(Math.random() * a.length), 0, a[e]);
}
}
return a;
}
console.log("Shuffled: " + shuffle([
[1, 2, 3, 4, 5],
[5, 4, 3, 2, 1]
]))
But it's not working as intended. Is their an easier way to do this? Or is my code correct and just buggy.

You can use Array.from() to create a new shallow-copied array and then to shuffle Array.prototype.sort() combined with Math.random()
Code:
const toShuffle = [
[1, 2, 3, 4, 5],
[9, 8, 7, 6, 5],
[10, 67, 19 ,27]
]
const shuffle = a => Array.from(a).sort(() => .5 - Math.random())
const result = toShuffle.map(shuffle)
console.log('Shuffled:', JSON.stringify(result))
console.log('To shuffle:', JSON.stringify(toShuffle))

You almost got it. The problem is that you are removing one item from an array, instead of capturing the removed item and them placing in a random position:
let toShuffle = [
[1, 2, 3, 4, 5],
[9, 8, 7, 6, 5],
[10, 67, 19 ,27]
];
function shuffle(a) {
a = [...a]; //clone array
for (let e in a) {
if (Array.isArray(a[e])) {
a[e] = shuffle(a[e]);
} else {
a.splice(~~(Math.random() * a.length), 0, a.splice(e, 1)[0]);
}
}
return a;
}
console.log(JSON.stringify(shuffle(toShuffle)))
console.log(JSON.stringify(toShuffle))
[EDIT]
The original code did not shuffle the parent array, if you need shuffle everything recursively, you can use this:
let toShuffle = [
[1, 2, 3, 4, 5],
[9, 8, 7, 6, 5],
[10, 67, 19 ,27]
];
function shuffle(a) {
a = a.map(i => Array.isArray(i) ? shuffle(i) : i); //clone array
a.sort(i => ~~(Math.random() * 2) - 1); //shuffle
return a;
}
console.log("shuffled", JSON.stringify(shuffle(toShuffle)))
console.log("original", JSON.stringify(toShuffle))

JavaScript move along all items in array by X number

I'm wanting to create a function which accepts 2 arguments, first argument is an array, second argument is a number of index positions to move all the array items.
So for example if I passed exampleFunc([1,2,3,4,5], 2) it should move all items 2 places to the right, so returns [4,5,1,2,3]. I've done the following, however is there a more eloquent / efficient way of doing this? Also if I wanted to reverse the direction and condense into 1 function and not two as done below, any suggestions how to do this other than putting conditionals around the different part of each function? Tried using .splice() method but didn't really got anywhere. Any help would really be appreciated!
const moveArrayPositionRight = (array, movePositions) => {
let newArray = new Array(array.length);
for (i = 0; i < array.length; i++) {
let newIndex = i - movePositions;
if (newIndex < 0) {
newIndex += array.length;
}
newArray[i] = array[newIndex];
}
return newArray;
};
console.log(moveArrayPositionRight([2, 4, 6, 8, 10], 2)); // output: [8, 10, 2, 4, 6]
const moveArrayPositionLeft = (array, movePositions) => {
let newArray = new Array(array.length);
for (i = 0; i < array.length; i++) {
let newIndex = i - movePositions;
if (newIndex < 0) {
newIndex += array.length - 1;
}
newArray[i] = array[newIndex];
}
return newArray;
};
console.log(moveArrayPositionLeft([3, 6, 9, 12, 15], 2)); // output: [9,12,15,3,6]

You have the index of the position where you want to slice the array up and rearrange it, so you can use .slice to do exactly that - extract the sub-arrays that need to be rearranged, and put into a new array:
const moveArrayPositionRight = (array, movePositions) => [
...array.slice(array.length - movePositions),
...array.slice(0, array.length - movePositions)
];
console.log(moveArrayPositionRight([2, 4, 6, 8, 10], 2)); // output: [8, 10, 2, 4, 6]
console.log(moveArrayPositionRight([2, 4, 6, 8, 10], 3)); // expected [6, 8, 10, 2, 4]
.slice can also take negative indicies to slice an amount from the end instead of from the beginning:
const moveArrayPositionRight = (array, movePositions) => [
...array.slice(-movePositions),
...array.slice(0, -movePositions)
];
console.log(moveArrayPositionRight([2, 4, 6, 8, 10], 2)); // output: [8, 10, 2, 4, 6]
console.log(moveArrayPositionRight([2, 4, 6, 8, 10], 3)); // expected [6, 8, 10, 2, 4]
Can also use .concat instead of spread
const moveArrayPositionRight = (array, movePositions) => array
.slice(array.length - movePositions)
.concat(array.slice(0, array.length - movePositions));
console.log(moveArrayPositionRight([2, 4, 6, 8, 10], 2)); // output: [8, 10, 2, 4, 6]
console.log(moveArrayPositionRight([2, 4, 6, 8, 10], 3)); // expected [6, 8, 10, 2, 4]
Same sort of thing for moveArrayPositionLeft:
const moveArrayPositionLeft = (array, movePositions) => [
...array.slice(movePositions),
...array.slice(0, movePositions)
];
console.log(moveArrayPositionLeft([3, 6, 9, 12, 15], 2)); // output: [9,12,15,3,6]

find the smallest number in a array of an array

i'm trying to write a function to find the smallest number on an array of an array.
already tryed this, but i don't really know how to do when there is arrays on an array.
const arr = [4, 8, 2, 7, 6, 42, 41, 77, 32, 9]
const min = Math.min(arr)
console.log(min)

By taking ES6, you could use the spread syntax ..., which takes an array as arguments.
const arr = [4, 8, 2, 7, 6, 42, 41, 77, 32, 9];
const min = Math.min(...arr);
console.log(min);
With ES5, you could take Function#apply, which take this and the parameters as array.
const arr = [4, 8, 2, 7, 6, 42, 41, 77, 32, 9];
const min = Math.min.apply(null, arr);
console.log(min);
For unflat arrays, take a flatten function, like
const
flat = array => array.reduce((r, a) => r.concat(Array.isArray(a) ? flat(a) : a), []),
array = [[1, 2], [3, 4]],
min = Math.min(...flat(array));
console.log(min);

You can use map to iterate over the nested arrays and then use Math.min(...array) on each to get the minimum. The output from map is an array of minimum values.
const arr = [[4, 8, 2], [7, 6, 42], [41, 77, 32, 9]];
const out = arr.map(a => Math.min(...a));
console.log(out);

Use spread ... and flat:
const a = [[0, 45, 2], [3, 6, 2], [1, 5, 9]];
console.log(Math.min(...a.flat()));
Or you might use reduce:
const arr = [[7, 45, 2], [3, 6, 2], [1, 5, 9]];
let r = arr.reduce((a, e) => Math.min(a, ...e), Infinity)
console.log(r);

Merge elements of array with comma with max counter

So I have an array of ids something like this:
const arr = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11];
I need a function that will be called like mergeArray(arr, 3), and it should return comma separated values with maximum of 3 elements like this:
const newArr = ['1,2,3', '4,5,6', '7,8,9', '10,11'];
How can I do this? If possible with ES6 functions for simpler code.

slice your array into 3 lengths arrays and directly join them
const arr = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11];
const mergeArray = (arr, size) => {
let res = [];
for (i = 0; i < arr.length; i += size) {
res.push(arr.slice(i, i + size).join(','));
}
return res;
}
console.log(mergeArray(arr, 3));

You can split() the array into the specific size and join() them before pushing into the resulting array:
const arr = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11];
var i, j, newArr=[], size = 3;
for (i=0,j=arr.length; i<j; i+=size) {
newArr.push(arr.slice(i, i+size).join());
}
console.log(newArr);

One of the ways to do it is with Array.prototype.reduce and Array.prototype.map:
const arr = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11];
function mergeArray(arr, n) {
return arr
.reduce((all, el, i) => {
const ind = Math.floor(i/n);
all[ind] = [...all[ind] || [], el]
return all;
},[])
.map(a => a.join(','))
}
console.log(mergeArray(arr, 3));

You could join the array and match the wanted parts with a regular expression.
var data = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11],
result = data.join(',').match(/\d+(,\d+(,\d+)?)?/g)
console.log(result);

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