create own sort() function in javascript

Question

I want to create my own sort() function on an array in javascript. The function should expect the following string elements in the list [0-9]*[A-Z][0-9]*[A-Z][0-9]* That means first there are arbitrary number of numbers 0-9, then there is One letter, followed by arbitrary numbers 0-9, then One Letter and then finally arbitrary numbers 0-9. Now I want to sort this list, but I want to sort it backwards on the Letters Only. That means that for example [xExCx,xQxEx,xSxEx,xSxFx] will become after its sorted [xSxFx,xSxEx,xQxEx,xExCx] where again x is an arbitrary number of numbers 0-9. It will sort on the first letter (backwards) first and then the second letter. So that letter E comes before an A. Perhaps anyone of you brilliant guys could give me a push in the right direction, I have only gotten this far.

function sortList(listOfNames) {
   var sortedListOfNames=new Array();
   for (i = 0; i < listOfNames.length; i++) { 
   //Sort listOfNames
   }
}

So you want a reverse sort on only the letters in the string? Do you want to completely ignore the values or quantity of numeric digits anywhere in the string? — jfriend00
– jfriend00, Commented Jul 6, 2014 at 9:02
Have you looked at the callback for sort? developer.mozilla.org/en/docs/Web/JavaScript/Reference/… If you can create a simple snippet of code that does your custom letter comparison, you can easily write a callback that sorts by it. — deceze
– deceze ♦, Commented Jul 6, 2014 at 9:02

jfriend00 · Accepted Answer · 2014-07-06 09:46:27Z

2

You can use the sorting logic already built into arrays and just apply a custom comparison function. Assuming that your sort algorithm is to disregard all numeric digits in the string and just do a reverse sort on the alpha characters left in the string, you can supply a sort callback function to the .sort() built into the Array object like this:

myArray.sort(function(a, b) {
    a = a.replace(/\d/g, "");
    b = b.replace(/\d/g, "");
    return b.localeCompare(a);        
});

This removes all the numeric digits from the two strings, then does a string comparison of the two and returns that result. The .sort() method then performs a sort based on that comparison algorithm. You can reverse the order of the sort by simply swapping a and b in the localeCompare() statement using either b.localeCompare(a) or a.localeCompare(b).

This could be made more efficient by pulling the regex out of the comparison function so it is just created once and reused on every comparison:

var nRegex = /\d/g;
myArray.sort(function(a, b) {
    a = a.replace(nRegex, "");
    b = b.replace(nRegex, "");
    return b.localeCompare(a);        
});

edited Jul 6, 2014 at 9:46

answered Jul 6, 2014 at 9:04

jfriend00

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2 Comments

anders Over a year ago

Thank you so much, exactly what I wanted =)

anders Over a year ago

Edit, never mind I check the function spec's instead.

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