Pushing data from a 1d array to a 2d array

Question

I'm trying to create a 2d array with the contents of a 1d array. The 2d array has the correct amount of rows and columns, however, each index of the 2d array contains the entirety of the original 1d array.

How can I turn the 1d array:

var OneD = [ "Bristol", "Cardiff", "Birmingham",
             "Luton", "Swansea", "Aberdeen",
             "Birmingham", "Manchester", "Southampton", 
             "Chester", "Swansea", "Brighton",
             "Portsmouth", "Bournemouth", "Glasgow", 
             "Newcastle", "Cardiff", "Bristol"];

Into this 2d array:

twoD = [
        ["Bristol", "Cardiff", "Birmingham", "Luton", "Swansea", "Aberdeen"],
        ["Birmingham", "Manchester", "Southampton", "Chester", "Swansea", "Brighton"],
        ["Portsmouth", "Bournemouth", "Glasgow", "Newcastle", "Cardiff", "Bristol"]
 ];

My Code

var twoD = [];
var rows = 3;
var cols = 6;

for (var i = 0; i < rows; i++) {
    twoD.push( [] );
}

for (var i = 0; i < rows; i++) {
    for (var j =  0; j < cols; j++) {
        twoD[i].push(oneD);
    }
}

console.log(twoD);

Possible duplicate of [Split array into chunks](https://stackoverflow.com/questions/8495687/split-array-into-chunks) — scraaappy, Aug 16 '18 at 20:17

score 1 · Accepted Answer · answered Aug 16 '18 at 19:58

Use a single for loop. On each iteration, add the cols number to i, and slice from the OneD array the items between i and i + cols. Push the sliced items into the twoD array.

var OneD = ["Bristol","Cardiff","Birmingham","Luton","Swansea","Aberdeen","Birmingham","Manchester","Southampton","Chester","Swansea","Brighton","Portsmouth","Bournemouth","Glasgow","Newcastle","Cardiff","Bristol"];

var twoD = [];
var cols = 6;

for(var i = 0; i < OneD.length; i += cols) {
  twoD.push(OneD.slice(i, i + cols));
}

console.log(twoD);

Elegant solution. Thank you. – JimmyNeedles Aug 16 '18 at 20:32 — JimmyNeedles, Aug 16 '18 at 20:32

Priya · Answer 2 · 2018-08-16T20:48:48.673

This way it can be done. But be sure to handle left out items. here the array length is exactly 3 parts for 6 items.

var OneD = ["Bristol", "Cardiff", "Birmingham",
  "Luton", "Swansea", "Aberdeen",
  "Birmingham", "Manchester", "Southampton",
  "Chester", "Swansea", "Brighton",
  "Portsmouth", "Bournemouth", "Glasgow",
  "Newcastle", "Cardiff", "Bristol"
];

var TwoD = [];
var cols = 6;
var rows = parseInt(OneD.length / cols, 10); // rows = 3
for (var i = 0; i < rows; i++) {
  TwoD.push(OneD.slice(i * cols, (i * cols + cols)));
}
console.log(TwoD);

(Or)

var OneD = ["Bristol", "Cardiff", "Birmingham",
  "Luton", "Swansea", "Aberdeen",
  "Birmingham", "Manchester", "Southampton",
  "Chester", "Swansea", "Brighton",
  "Portsmouth", "Bournemouth", "Glasgow",
  "Newcastle", "Cardiff", "Bristol"
];

var TwoD = OneD.join(',').match(/([^,]*,[\w]*){5}[,]*/g).map(function(i) {return i.replace(/,$/, '').split(/,/);});

console.log(TwoD);

Barmar · Answer 3 · 2018-08-16T20:13:34.517

Your second loop is pushing all of OneD every time. You need to index the array.

var oneD = ["Bristol","Cardiff","Birmingham","Luton","Swansea","Aberdeen","Birmingham","Manchester","Southampton","Chester","Swansea","Brighton","Portsmouth","Bournemouth","Glasgow","Newcastle","Cardiff","Bristol"];

var twoD = [];
var cols = 6;
var rows = 3;

for (var i = 0; i < rows; i++) {
    twoD.push( [] );
}

for (var i = 0; i < rows; i++) {
    for (var j =  0; j < cols; j++) {
        twoD[i].push(oneD[i * cols + j]);
    }
}

console.log(twoD);

You can also combine the two loops into one. And also get rid of the index calculation by making the outer loop increment by the number of columns. The version below also doesn't require the 1d array to be exactly rows * cols in length.

var oneD = ["Bristol","Cardiff","Birmingham","Luton","Swansea","Aberdeen","Birmingham","Manchester","Southampton","Chester","Swansea","Brighton","Portsmouth","Bournemouth","Glasgow","Newcastle","Cardiff","Bristol"];

var twoD = [];
var cols = 6;
var rows = 3;

for (var i = 0; i < oneD.length; i += cols) {
    var row = [];
    var maxColIndex = Math.min(i+cols, oneD.length);
    for (var j =  i; j < maxColIndex; j++) {
        row.push(oneD[j]);
    }
    twoD.push(row);
}

console.log(twoD);

Pushing data from a 1d array to a 2d array

3 Answers3