Optimal method for iterating through this array efficiently using Javascript in Chrome version 36

Question

Optimal method for iterating through this array efficiently using Javascript in Chrome version 36

My array is quite large, resembling the following:

var counts = ["gfdg 34243", "jhfj 543554", ....] // With a length of 55268 elements

This is my current loop:

var replace = "";
var scored = 0;
var qgram = "";
var score1 = 0;
var len = counts.length;

function score(pplaintext1) {
    qgram = pplaintext1;
    for (var x = 0; x < qgram.length; x++) {
        for (var a = 0, len = counts.length; a < len; a++) {
            if (qgram.substring(x, x + 4) === counts[a].substring(0, 4)) {
                replace = parseInt(counts[a].replace(/[^1-9]/g, ""));
                scored += Math.log(replace / len) * Math.LOG10E;
            } else {
                scored += Math.log(1 / len) * Math.LOG10E;
            }
        }
    }
    score1 = scored;
    scored = 0;
} // This function needs to be called roughly 1000 times

I need to iterate through this array multiple times and my code is slowing down. I'm wondering what would be the most efficient way to iterate through this array to maximize time savings.

javascript arrays loops

Answer 1

Answer №1

Your list of unique strings and values in the `counts` array can be optimized by using an object instead, where the unique strings act as keys:

var counts = { gfdg: 34243, jhfj: 543554, ... };

This change will significantly enhance performance by eliminating the need for an inner loop with a time complexity of O(n) and replacing it with constant-time lookup using object keys (O(1)).

In addition, it's recommended to avoid divisions like `log(1 / n) = -log(n)` and move loop invariants outside the loops. The expression `log(1/len) * Math.LOG10E` adds a constant value in each pass except in the first `if` statement branch, where you must also consider `Math.log(replace)` which means adding it in logarithmic calculations.

Furthermore, try not to rely on state variables from the outer scope for scoring purposes. You can refactor your scoring algorithm like this:

var len = Object.keys(counts).length;

function score(text) {
    var result = 0;
    var factor = -Math.log(len) * Math.LOG10E;

    for (var x = 0, n = text.length - 4; x < n; ++x) {
        var qgram = text.substring(x, x + 4);
        var replace = counts[qgram];
        if (replace) {
            result += Math.log(replace) + factor;
        } else {
            result += len * factor;  // once for each ngram
        }
    }
    return result;
}

Answer 2

Your list of unique strings and values in the `counts` array can be optimized by using an object instead, where the unique strings act as keys:

var counts = { gfdg: 34243, jhfj: 543554, ... };

This change will significantly enhance performance by eliminating the need for an inner loop with a time complexity of O(n) and replacing it with constant-time lookup using object keys (O(1)).

In addition, it's recommended to avoid divisions like `log(1 / n) = -log(n)` and move loop invariants outside the loops. The expression `log(1/len) * Math.LOG10E` adds a constant value in each pass except in the first `if` statement branch, where you must also consider `Math.log(replace)` which means adding it in logarithmic calculations.

Furthermore, try not to rely on state variables from the outer scope for scoring purposes. You can refactor your scoring algorithm like this:

var len = Object.keys(counts).length;

function score(text) {
    var result = 0;
    var factor = -Math.log(len) * Math.LOG10E;

    for (var x = 0, n = text.length - 4; x < n; ++x) {
        var qgram = text.substring(x, x + 4);
        var replace = counts[qgram];
        if (replace) {
            result += Math.log(replace) + factor;
        } else {
            result += len * factor;  // once for each ngram
        }
    }
    return result;
}

Optimal method for iterating through this array efficiently using Javascript in Chrome version 36

Answer №1

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