How do you split an array into array pairs in JavaScript?

Question

I want to split an array into pairs of arrays.

var arr = [2, 3, 4, 5, 6, 4, 3, 5, 5]

would be

var newarr = [
    [2, 3],
           


        

Answer 1

Lodash has a method for this: https://lodash.com/docs/4.17.10#chunk

_.chunk([2,3,4,5,6,4,3,5,5], 2); // => [[2,3],[4,5],[6,4],[3,5],[5]]

Answer 2

This combines some of the answers above but without Object.fromEntires. The output is similar to what you would get with minimist.

    const splitParameters = (args) => {
      const split = (arg) => (arg.includes("=") ? arg.split("=") : [arg]);
    
      return args.reduce((params, arg) => [...params, ...split(arg)], []);
    };
    
    const createPairs = (args) =>
      Array.from({ length: args.length / 2 }, (_, i) =>
        args.slice(i * 2, i * 2 + 2)
      );
    
    const createParameters = (pairs) =>
      pairs.reduce(
        (flags, value) => ({
          ...flags,
          ...{ [value[0].replace("--", "")]: value[1] }
        }),
        {}
      );
    
    const getCliParameters = (args) => {
      const pairs = createPairs(splitParameters(args));
      const paramaters = createParameters(pairs);
    
      console.log(paramaters);
    
      return paramaters;
    };
 

    //const argsFromNodeCli = process.argv.slice(2); // For node
      
    const testArgs = [
      "--url",
      "https://www.google.com",
      "--phrases=hello,hi,bye,ok"
    ];
    
    const output = getCliParameters(testArgs);
    document.body.innerText = JSON.stringify(output);

Answer 3

It's possible to group an array into pairs/chunks in one line without libraries:

function chunks(arr, size = 2) {
  return arr.map((x, i) => i % size == 0 && arr.slice(i, i + size)).filter(x => x)
}
console.log(chunks([1, 2, 3, 4, 5, 6, 7])) // -> [[1, 2], [3, 4], [5, 6], [7]]

Answer 4

A slightly different approach than using a for loop for comparison. To avoid modifying the original array slice makes a shallow copy since JS passes objects by reference.

function pairArray(a) {
  var temp = a.slice();
  var arr = [];

  while (temp.length) {
    arr.push(temp.splice(0,2));
  }

  return arr;
}

var array = [2,3,4,5,6,4,3,5,5];
var newArr = pairArray(array);

function pairArray(a) {
  var temp = a.slice();
  var arr = [];

  while (temp.length) {
    arr.push(temp.splice(0,2));
  }

  return arr;
}

document.write('<pre>' + JSON.stringify(newArr) + '</pre>');

Answer 5

Here is a short and more generic solution:

function splitArrayIntoPairs(arr, n) {
 var len = arr.length
  var pairs = []

  for (let i = 0; i < len; i += n) {
    var temp = []
    for (var j = i; j < (i + n); j++) {
      if (arr[j] !== undefined) {
        temp.push(arr[j])
      }
    }
    pairs.push(temp)
  }
  return pairs
}

Where arr is your array and n is no of pairs

Answer 6

Here's a good generic solution:

function splitInto(array, size, inplace) {
    var output, i, group;

    if (inplace) {
        output = array;

        for (i = 0; i < array.length; i++) {
            group = array.splice(i, size);

            output.splice(i, 0, group);
        }
    } else {
        output = [];

        for (i = 0; i < array.length; i += size) {
            output.push(array.slice(i, size + i));
        }
    }

    return output;
}

For your case, you can call it like this:

var arr= [2,3,4,5,6,4,3,5,5];
var newarr = splitInto(arr, 2);

The inplace argument determines whether the operation is done in-place or not.

Here's a demo below:

function splitInto(array, size, inplace) {
    var output, i, group;

    if (inplace) {
        output = array;

        for (i = 0; i < array.length; i++) {
            group = array.splice(i, size);

            output.splice(i, 0, group);
        }
    } else {
        output = [];

        for (i = 0; i < array.length; i += size) {
            output.push(array.slice(i, size + i));
        }
    }

    return output;
}

var arr= [2,3,4,5,6,4,3,5,5];
var newarr = splitInto(arr, 2);

disp(newarr);

// or we can do it in-place...
splitInto(arr, 3, true);

disp(arr);

function disp(array) {  
  var json = JSON.stringify(array);

  var text = document.createTextNode(json);
  var pre = document.createElement('pre');

  pre.appendChild(text);
  document.body.appendChild(pre);
}