Split Array into Two-Dimensional Array: Is There a Better Solution?

Question

I solved an algorithm challenge from FreeCodeCamp with the function below, but am wondering if this is a "good" way to solve the problem, most specifically, because I am setting my counter to i+=0 and splicing indices from the head. Have I created an anti-pattern here? Is there anything that would be more logical, and can you explain why? Thank you in advance for help!

function chunk(arr, size) {
  var newArr = [];
  for (i=0; i<arr.length; i+=0) { 
      var sliced = arr.slice(i, size);
      newArr.push(sliced);
      arr.splice(0, size);
  }
  return newArr;
}
chunk([0, 1, 2, 3, 4, 5, 6, 7, 8], 4);
returns--> [ [ 0, 1, 2, 3 ], [ 4, 5, 6, 7 ], [ 8 ] ]

You can look into Array.slice(). Also if objective of this question is to seek improvements, you should try CodeReviews instead — Rajesh Dixit
– Rajesh Dixit, Commented Feb 26, 2016 at 16:23
I'm voting to close this question as off-topic because it is asking for a codereview. ask on codereview.stackexchange.com — Daniel A. White
– Daniel A. White, Commented Feb 26, 2016 at 16:29

Thomas · Accepted Answer · 2016-02-27 09:58:29Z

Have I created an anti-pattern here? Is there anything that would be more logical, and can you explain why?

your code contains a few improvable parts

function chunk(arr, size) {
  //newWhatever, myWhatever, ... look for a better naming like `out` or `result` 
  //or in this case `chunks` would describe the content of the variable
  var newArr = [];

  //you initialize `i` without the var-keyword, therefore you populate/pollute the global namespace
  //and instead of calculating i+=0, you can leave this part empty:
  //for(var i=0; i<arr.length; ){
  for (i=0; i<arr.length; i+=0) { 
      var sliced = arr.slice(i, size);
      newArr.push(sliced);

      //splicing (with P) is often a thing that should be avoided, 
      //- it is destructive (it destroys the input-array)
      //- it is slow, cause the engine has to allocate new memory 
      //  and copy the remaining elements over to this memory,
      //  and garbage-collect the old memory
      arr.splice(0, size);
  }
  return newArr;
}

a better solution would be:

function chunk(arr, size) {
    for(var chunks=[], i=0; i<arr.length; i+=size)
        chunks.push(arr.slice(i, size));
    return chunks;
}

assuming that the inputs are right.

For completenes, you should add some validation of the inputs. That arr is in place, can be sliced, and has a length-property.
And that size is an integer > 0 otherwise the code may create strange results.

function chunk(arr, size) {
    //checks if arr is not empty and arr.slice is not empty 
    //and casts the length-property to int
    //if anything "fails" len = 0;
    var len = (arr && arr.slice && arr.length)|0;

    //check if size is > 1 and is an integer
    if(size !== Math.floor(size) || size < 1)
        throw new Error("invalid chunl-size: "+size);

    for(var chunks=[], i=0; i<len; i+=size)
        chunks.push(arr.slice(i, size));
    return chunks;
}

Andy · Accepted Answer · 2016-02-26 16:29:20Z

1

Recursion, perhaps?

function chunk(arr, size, out) {

  // if the output array hasn't been passed in
  // create it
  out = out || [];

  // if there are no elements in the input array
  // return the output array
  if (!arr.length) return out;

  // push the "head" of the input array to the
  // output array
  out.push(arr.slice(0, size));

  // call chunk again with the "tail" of the input array
  return chunk(arr.slice(size), size, out);
}

DEMO

answered Feb 26, 2016 at 16:29

Andy

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Comments

Nour Sammour · Accepted Answer · 2016-02-26 16:34:15Z

0

function chunk(arr, size) {
    var subArrayCount = arr.length / size;
    var res = [];
    for (i = 0; i < subArrayCount; i++) {
        var from = size * i;
        var to = (size * (1 + i));
        console.log(to)
        var sliced = arr.slice(from, to);
        res.push(sliced);
    }
    return res;
}
chunk([0, 1, 2, 3, 4, 5, 6, 7, 8], 4);
returns--> [ [ 0, 1, 2, 3 ], [ 4, 5, 6, 7 ], [ 8 ] ]

answered Feb 26, 2016 at 16:34

Nour Sammour

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