Processing an array by sub arrays

Question

Suppose we have an array of variable length, and I want to process it by chunks that are of a maximum length of 100, and do it in the minimum number of chunks. So for an array of length 241, it would be 3 sub arrays of sizes 41, 100, 100 (or 100, 100, 41).

curr_len = arr.length;
offset = curr_len%100;
doSomethingWithSubArray(arr.slice(offset))

for(j = offset; j <= curr_len; j = j+100){
    doSomethingWithSubArray(arr.slice(j,j+100))
}

I'm sure there are more elegant ways of doing this, possibly without the special case before the for loop. Any ideas?

Bergi · Accepted Answer · 2012-07-26 15:56:34Z

2

I'd expect the last chunk to be of smaller size. The code then would be:

for (var i=0; i<arr.length; i+=100)
    doSomethingWithSubArray(arr.slice(i, 100));

This is exactly what my splitBy function does:

Array.prototype.splitBy = function(n) {
/* get: number of items per array
return: array of n-sized arrays with the items (last array may contain less then n) */
    for (var r=[], i=0; i<this.length; i+=n)
        r.push(this.slice(i, i+n));
    return r;
}

Then write only:

arr.splitBy(100).forEach(doSomethingWithSubArray);

edited Jul 26, 2012 at 15:56

answered Jul 26, 2012 at 15:49

Bergi

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2 Comments

leonsas Over a year ago

Of course. For some reason, my brain was avoiding this to avoid an IndexOutOfRange. I guess javascript is wonderful.

blueiur Over a year ago

my solution is consice better yours how about this?

Hacker Wins · Accepted Answer · 2012-07-26 15:50:49Z

1

use chunk function~

function chunk(a, s){
    for(var x, i = 0, c = -1, l = a.length, n = []; i < l; i++)
        (x = i % s) ? n[c][x] = a[i] : n[++c] = [a[i]];
    return n;
}

console.log(chunk([1,2,3,4,5,6,7,8,9,10], 3));

answered Jul 26, 2012 at 15:50

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Comments

blueiur · Accepted Answer · 2012-07-30 14:04:25Z

1

it's functional style recursive solutions. no var, no loop, no count, because it's more cleary

var chunk = function(arr, n){
    if (arr.length == 0) return [];
    var head = arr.slice(0, n), rest = arr.slice(n);

    return [head].concat( chunk(rest, n) );
};

console.log(chunk([1,2,3,4,5,6,7,8,9,10], 3));

answered Jul 30, 2012 at 14:04

blueiur

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1 Comment

Bergi Over a year ago

No "var" is not really true :-) However, most people understand loops easier than recursive calls - and they're faster, too.

Esailija · Accepted Answer · 2012-07-26 15:49:22Z

0

Not really, using reduce looks like this:

var array = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11];

var splitArrays = array.reduce(function(arr, cur, i) {
    if (i % 3 === 0) arr.push([]);
    arr[i / 3 | 0].push(cur);
    return arr;
}, []);
//splitArrays looks like:
//[[1,2,3],[4,5,6],[7,8,9],[10,11]]

More generic function

function splitArray(array, num) {
    return array.reduce(function(arr, cur, i) {
        if (i % num === 0) arr.push([]);
        arr[i / num | 0].push(cur);
        return arr;
    }, []);
}

answered Jul 26, 2012 at 15:49

Esailija

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Comments

Oleg V. Volkov · Accepted Answer · 2012-07-26 15:51:05Z

0

Make your doSomethingWithSubArray function accept a starting index and return a next unprocessed index or null if there's no more work. Put this "iterator" in a while loop. Do rest of work that you want to do between chunks (update UI?) right after calling this "iterator" in a while condition.

answered Jul 26, 2012 at 15:51

Oleg V. Volkov

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