Chunking array within array algorithm

Question

first question on stackoverflow, i'm struggling with this algorithm. This is supposed to slice my array in 5 like "[[0, 1], [2, 3], [4, 5], [6, 7], [8]]" but all i got is "[ [ 0, 1 ], [ 2, 3 ], [ 4, 5 ], [ 6, 7, 8 ] ]"

function chunkArrayInGroups(arr, size) {
  var newArr = [];
  console.log(Math.floor(arr.length / size));
  for (i = 0; i <= (Math.floor(arr.length / size)) + 1; ++i) {
    var cut = size;
    newArr.push(arr.splice(0, cut));
  }
  if (arr.length > 0) {
    newArr.push(arr.splice(0, size + (arr.length - size)));
  }
  return newArr;
}
chunkArrayInGroups([0, 1, 2, 3, 4, 5, 6, 7, 8], 2);
// expected - [[0, 1], [2, 3], [4, 5], [6, 7], [8]]

If you have any tips about the way of asking questions, i'd be happy to receive any advice !

Welcome to stackoverflow !. This might help you stackoverflow.com/help/how-to-ask get started on how to as a question here on stackoverflow. — thebenman
– thebenman, Commented Dec 1, 2016 at 19:52
your algorithm is not working because of this line: for (i = 0; i <= (Math.floor(arr.length / size)) + 1; ++i) {...} witch is for (i = 0; i <= (Math.floor(9 / 2)) + 1; ++i) {...}, initially Math.floor(arr.length / size) is equal 5 but after each execution you shrink your arr.length by size so now you have for (i = 1; i <= (Math.floor(7 / 2)) + 1; ++i) {...} then for (i = 2; i <= (Math.floor(5 / 2)) + 1; ++i) {...} and for (i = 3; i <= (Math.floor(3 / 2)) + 1; ++i) {...} is not going to execute. So you do only 3 executions instead of 5. Hope that makes sense. — brigysl
– brigysl, Commented Dec 1, 2016 at 22:37
@brigysl Yes thank you ! I forgot this one.. splice is dangerous ! — Mike
– Mike, Commented Dec 1, 2016 at 22:40

Ori Drori · Accepted Answer · 2016-12-01 19:59:03Z

2

Use a simple for loop with Array#slice, because slice doesn't change the length of the original array:

function chunkArrayInGroups(arr, size) {
  var chunked = [];
  
  for(var i = 0; i < arr.length; i += size) { // increment i by the size
    chunked.push(arr.slice(i, i + size));
  }
  
  return chunked;
}

var result = chunkArrayInGroups([0, 1, 2, 3, 4, 5, 6, 7, 8], 2);

console.log(result);

edited Dec 1, 2016 at 19:59

answered Dec 1, 2016 at 19:48

Ori Drori

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1 Comment

Mike Over a year ago

I thought the last .slice() must perfectly fit the array index, in this case (0, 1) :o It worked perfectly, thank you !

Pranav C Balan · Accepted Answer · 2016-12-01 19:54:31Z

1

Since you are removing element using Array#splice the array length get decreased so instead of calculating the range cache the range for the for loop condition. Although use Math.ceil and avoid the unnecessary if statement.

function chunkArrayInGroups(arr, size) {
  var newArr = [],
    range = Math.ceil(arr.length / size);

  for (i = 0; i < range; i++) {
    newArr.push(arr.splice(0, size));
  }

  return newArr;
}
console.log(chunkArrayInGroups([0, 1, 2, 3, 4, 5, 6, 7, 8], 2));

edited Dec 1, 2016 at 19:54

answered Dec 1, 2016 at 19:45

Pranav C Balan

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1 Comment

Mike Cluck Over a year ago

Care to explain to OP why?

Lahar Shah · Accepted Answer · 2016-12-01 19:48:50Z

0

Check this out.

function chunkArrayInGroups(arr, size) {
     newArr = [];
     for (i=0,j=arr.length; i<j; i+=size) {
        newArr.push(arr.slice(i,i+size));
     }
    return newArr;
}
console.log(chunkArrayInGroups([0, 1, 2, 3, 4, 5, 6, 7, 8], 2));
// expected - [[0, 1], [2, 3], [4, 5], [6, 7], [8]]

answered Dec 1, 2016 at 19:48

Lahar Shah

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Comments

Tomalak · Accepted Answer · 2016-12-01 20:02:38Z

0

Another way to do it is Array#reduce:

function chunkArrayInGroups(arr, size) {
    return arr.reduce(function (accum, elem) {
        var curr = accum[accum.length - 1];
        if (curr.length < size) curr.push(elem); else accum.push([elem]);
        return accum;
    }, [[]]);
}

var result = chunkArrayInGroups([0, 1, 2, 3, 4, 5, 6, 7, 8], 2);
console.log( JSON.stringify(result) );

answered Dec 1, 2016 at 20:02

Tomalak

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Comments

brigysl · Accepted Answer · 2016-12-01 20:46:16Z

0

Welcome to SO. Here is how I would do that. Let me know if you have any questions about this approach.

function chunkArrayInGroups(arr, size) {
  var newArr = [];
  while(arr.length > 0){
    newArr.push(arr.splice(0, size)); 
  }
  return newArr;
}

edited Dec 1, 2016 at 20:46

answered Dec 1, 2016 at 20:32

brigysl

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Comments

Redu · Accepted Answer · 2016-12-02 17:34:04Z

0

Functionally you can do as follows;

function chunkArrayInGroups(a,g){
  return Array(Math.ceil(a.length/g)).fill()
                                     .map((_,i) => [a[g*i]].concat(a.slice(g*i+1, g*i+g)));
}

var arr = [0, 1, 2, 3, 4, 5, 6, 7, 8];
 result = [];

result = chunkArrayInGroups(arr,2);
console.log(JSON.stringify(result));

result = chunkArrayInGroups(arr,3);
console.log(JSON.stringify(result));

result = chunkArrayInGroups(arr,4);
console.log(JSON.stringify(result));

answered Dec 2, 2016 at 17:34

Redu

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Comments

Nina Scholz · Accepted Answer · 2017-08-17 12:15:09Z

0

You could use a while loop and splice the length of the wanted size for a grouped array.

function chunkArrayInGroups(array, size) {
    var result = [];
    while (array.length) {
        result.push(array.splice(0, size));
    }
    return result;
}

console.log(chunkArrayInGroups([0, 1, 2, 3, 4, 5, 6, 7, 8], 2));

edited Aug 17, 2017 at 12:15

answered Dec 2, 2016 at 15:34

Nina Scholz

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