Regex for extracting separate letters in a loop with javascript

Question

I'm working on a script to create metrics for online author identification. One of the things I came across in the literature is to count the frequency of each letter (how many a's, how many b's, etc) independent of upper or lower case. Since I don't want to create a separate statement for each letter, I'm trying to loop the thing, but I can't figure it out. The best I have been able to come up with is converting the ASCII letter code in to hex, and then...hopefully a miracle happens.

So far, I've got

element = id.toLowerCase();
var hex = 0;
for (k=97; k<122; k++){
    hex = k.toString(16); //gets me to hex
    letter = element.replace(/[^\hex]/g, "")//remove everything but the current letter I'm looking for
    return letter.length // the length of the resulting string is how many times the ltter came up
}

but of course, when I do that, it interprets hex as the letters h e x, not the hex code for the letter I want.

This is not the best approach; look at @ElliotBonneville's answer. But to answer the specific question, if you want to build a regex from variable components, use new RegExp(string) instead of a regex literal: var hexRegex = new RegExp("[^\\" + hex + "]", "g"); — Mark Reed
– Mark Reed, Commented Apr 23, 2012 at 19:03
@MarkReed: You might need to escape your string if you want to do that with general characters. — hugomg
– hugomg, Commented Apr 23, 2012 at 19:15

Elliot Bonneville · Accepted Answer · 2012-04-23 18:58:52Z

5

Not sure why you'd want to convert to hex, but you could loop through the string's characters and keep track of how many times each one has appeared with an object used as a hash:

var element = id.toLowerCase();
var keys = {};

for(var i = 0, len = element.length; i<len; i++) {
    if(keys[element.charAt(i)]) keys[element.charAt(i)]++;
    else keys[element.charAt(i)] = 1;
}

You could use an array to do the same thing but a hash is faster.

answered Apr 23, 2012 at 18:58

Elliot Bonneville

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4 Comments

hugomg Over a year ago

You can also use element.charCodeAt() if you feel like using numeric codes.

Elliot Bonneville Over a year ago

There's really no reason to as you'd just have to convert back to see which character is which, but yes, that's easily doable.

bigbenbt Over a year ago

wow. That's much slicker than what I was trying. I'm coming at this from a Matlab and mathematica background, so going this way never occurred to me. Thanks.

Elliot Bonneville Over a year ago

@bigbenbt: If this answer is useful to you, please mark it as accepted with the checkmark to the right of it. =)

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