Natural Array Element Sorting: Strings with Numbers

This article delves into the task of sorting arrays containing elements that combine strings and numbers in a natural order, where numerical sequences within the strings should be considered in the sorting process.

The Problem

Consider an array like this:

["IL0 Foo", "PI0 Bar", "IL10 Baz", "IL3 Bob says hello"]

If we attempt to sort this array using a conventional sort function, we may end up with an incorrect order:

["IL0 Foo", "IL10 Baz", "IL3 Bob says hello", "PI0 Bar"]

The Solution: Natural Sorting

To achieve natural sorting, we can leverage the following JavaScript function:

function naturalCompare(a, b) {
    var ax = [], bx = [];

    a.replace(/(\d )|(\D )/g, function(_, $1, $2) { ax.push([$1 || Infinity, $2 || ""]) });
    b.replace(/(\d )|(\D )/g, function(_, $1, $2) { bx.push([$1 || Infinity, $2 || ""]) });
    
    while(ax.length && bx.length) {
        var an = ax.shift();
        var bn = bx.shift();
        var nn = (an[0] - bn[0]) || an[1].localeCompare(bn[1]);
        if(nn) return nn;
    }

    return ax.length - bx.length;
}

This function tokenizes the input strings into arrays of numerical and non-numerical values. It then compares the arrays lexicographically, taking into account the numerical values as integers and the non-numerical values as strings.

Example

Applying this function to the given array results in the desired natural sorting order:

test = [
    "img12.png",
    "img10.png",
    "img2.png",
    "img1.png",
    "img101.png",
    "img101a.png",
    "abc10.jpg",
    "abc10",
    "abc2.jpg",
    "20.jpg",
    "20",
    "abc",
    "abc2",
    ""
];

test.sort(naturalCompare)
document.write("<pre>"   JSON.stringify(test,0,3));

This produces the following sorted array:

[
  "",
  "abc",
  "abc2",
  "abc10",
  "abc10.jpg",
  "20",
  "20.jpg",
  "img1.png",
  "img2.png",
  "img10.png",
  "img12.png",
  "img101.png",
  "img101a.png"
]