带有数组的数组：如何使用javascript将所有元素向前推送一个

Question

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.

Answer 1

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(' '))); 

Answer 2

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); 

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Answer 3

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) 

Answer 4

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) 

Answer 5

 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]] 

Answer 6

Assuming all your elements are numbers, you can do it like this:

1. Prepend i to the array
2. Flatten the array
3. Convert the array to a comma-separated string
4. Split the string into chunks of at most 3 numeric substrings (2 commas)
5. Convert the chunks back into arrays of numbers

 const 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 ); 

Answer 7

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)));