# Sparse arrays vs full arrays

## JavaScript performance comparison

Revision 9 of this test case created

## Preparation code

`` <script>  Benchmark.prototype.setup = function() {    var n, N, i, I, sparse = [],        full = [],        full2 = [];        N = 16384;    I = 8;        for (i = 0; i < I; i++) {      do {        n = (N * Math.random()) | 0;        if (n > (N - 1)) {          n = N - 1;        }      } while (sparse[n]);      sparse[n] = -100 + 200 * Math.random();    }    full.length = N;    full2.length = N;    for (i = 0; i < N; i++) {      if (typeof sparse[i] === "number") {        full[i] = sparse[i];        full2[i] = sparse[i];      } else {        full[i] = 0;        full2[i] = -100 + 200 * Math.random();      }    }  };</script>``

## Test runner

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Testing in unknown unknown
Test Ops/sec
Sparse array sum
``var sum = 0;sparse.forEach(function(v, i) {  sum += v;});``
pending…
Full array sum
``var len = full.length;sum = 0;for (i = 0; i < len; i++) {  sum += full[i];}``
pending…
Running sparse on full array
``var sum = 0;full.forEach(function(v, i) {  sum += v;});``
pending…
Sum all elements on a full array without zeros
``var len = full2.length;sum = 0;for (i = 0; i < len; i++) {  sum += full2[i];}``
pending…
Sparse array sum (using "for-in")
``var sum = 0;var k;for (k in sparse) {  sum += sparse[k];}``
pending…

## Revisions

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# 1 comment

Stefan K. commented :

Added a version that uses a for-in loop to sum the sparse array, which seems to be -much- faster in Firefox 21.

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