This is my array of arrays:
arr_1 = [1,2,3]
arr_2 = [4,5,6]
arr_3 = [7,8,9]
arr = [arr_1, arr_2, arr_3]
arr = [[1,2,3], [4,5,6], [7,8,9]]
What I want to do is push all elements like so that the final array is like the following and insert another element at the beginning of my array:
arr = [[i,1,2], [3,4,5], [6,7,8], [9]]
All sub-arrays must not be more than 3 elements.
Thanks for your help.
You could visit all inner arrays and unshift the leftover values from the previous loop.
var array = [[1, 2, 3], [4, 5, 6], [7, 8, 9]],
chunk = 3,
item = 'x',
i = 0,
temp = [item];
while (i < array.length) {
array[i].unshift(...temp);
temp = array[i].splice(chunk, array[i].length - chunk);
i++;
}
if (temp.length) {
array.push(temp);
}
console.log(array.map(a => a.join(' ')));
unshift and splice, but it seems to run an order of magnitude faster than the other answers.You can use the function reduce
var arr = [[1,2,3], [4,5,6], [7,8,9]],
newElem = "newOne",
all = [newElem, ...arr.reduce((a, c) => [...a, ...c], [])], // All together
// Build the desired output asking for the result of:
// element mod 3 === 0
result = all.reduce((a, c, i) => {
if (i % 3 === 0) a.push([c]);
else a[a.length - 1].push(c);
return a;
}, []);
console.log(result);.as-console-wrapper { max-height: 100% !important; top: 0; }
You could move on each iteration last element from previous array to next one and if the last sub-array has more then 3 elements then remove the last one and add it to new array.
let arr_1 = [1, 2, 3],
arr_2 = [4, 5, 6],
arr_3 = [7, 8, 9],
arr = [arr_1, arr_2, arr_3]
setInterval(function() {
const last = arr.length - 1;
const newElement = parseInt(Math.random() * 30)
arr.forEach((a, i) => {
if(i == 0) a.unshift(newElement);
if(arr[i + 1]) arr[i + 1].unshift(a.pop())
else if(arr[last].length > 3) arr[last + 1] = [arr[last].pop()]
})
console.log(JSON.stringify(arr))
}, 1000)You can do this quite succinctly with a simple unravel/ravel. It easy to adjust group size too.
let arr = [ [1,2,3], [4,5,6], [7,8,9]]
let newEl = 0
let groupSize = 3
var newArr = [];
var unravelled = arr.reduce((a, c) => a.concat(c), [newEl])
while(unravelled.length) newArr.push(unravelled.splice(0,groupSize));
console.log(newArr)arr_1 = [1, 2, 3]
arr_2 = [4, 5, 6]
arr_3 = [7, 8, 9]
arr = [
[1, 2, 3],
[4, 5, 6],
[7, 8, 9]
]
function reassignChunk(x) {
// create an array which will be used to store unwrapped values
var newArray = [];
arr.forEach(function(elem) {
newArray.push(...elem); //using spread operator to unwrap values
});
newArray.unshift(x, limit)
var modArray = [];
var m, j, temparray, chunk = 3;
for (m = 0; m < newArray.length; m = m + limit) {
// creatinging new array using slice
modArray.push(newArray.slice(m, m + limit));
}
console.log(modArray)
}
reassignChunk(13, 3)arr = [[i,1,2], [3,4,5], [6,7,8], [9]]Assuming all your elements are numbers, you can do it like this:
i to the arrayconst arr_1 = [1,2,3];
const arr_2 = [4,5,6];
const arr_3 = [7,8,9];
const i = 42;
const result = [i,...arr_1,...arr_2,...arr_3].join()
.match(/(?:[^,]+(,|$)){1,2}[^,]*/g).map( x => x.split(',').map(Number) )
;
console.log( result );You may do your 2d unshifting simply as follows;
var arr_1 = [1,2,3],
arr_2 = [4,5,6],
arr_3 = [7,8,9],
arr = [arr_1, arr_2, arr_3],
us2d = (a2d,...is) => is.concat(...a2d)
.reduce((r,e,i) => (i%3 ? r[r.length-1].push(e)
: r.push([e]), r), []);
console.log(JSON.stringify(us2d(arr,0)));
console.log(JSON.stringify(us2d(arr,-2,-1,0)));
