Table of contents
- Remove Duplicate Chars from a String
- Comparison: Remove Duplicate Chars from a String Via Array and RegExp
This post is about how to remove duplicate characters from a string. And what I mean is that I want to make every char unique.
Ex: “aabbbcccaadddee” will become “abcde“.
In “short words” the following steps are taken:
- Split the string to an array (source array)
- Create a second empty array which will retain the unique values
- Sort the source array with case insensitive
- Store current value for comparison
- Walk through the whole source array and for each character check if is the same with current value variable - if it is that character is not already added we add it to the second array (this because the source array is sorted and there cannot be an array like this after sorting:
array("a","b","a")
but only sorted… like this:
array("a","a","b")
- Join back the second array to a string
These are the steps and here is a function in Actionscript 3:
private function removeDuplicates(string:String):String { var arr:Array = string.split(''); var currentValue:String = ""; var tempArray:Array = new Array(); arr.sort(Array.CASEINSENSITIVE); arr.forEach( function(item:*,index:uint,array:Array):void { if (currentValue != item) { tempArray.push(item); currentValue = item; } } ); return tempArray.sort(Array.CASEINSENSITIVE).join(''); }
I tried to have the same result using regular expressions but no success. And I stress that I meant about removing duplicates and making a unique chars string. Removing only duplicates is easy and I can put a regular expression here for that but that is not the purpose of this article.
If anyone resolved this using RegExp please share :).
Popularity: 54%
Tags: ActionScript, Regexp, sorting, string
This post was written by Andrei Ionescu
Views: 4448
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[…] for. In fact, while searching for “php remove repeating character in string,” the first article listed in Google included a note at the bottom stating: “I tried to have the same result […]
Hello. Great post. It lead me to find the regex solution I was looking for. I mentioned your post as well as a possible regex solution to what you were looking for here:
http://www.ilovebonnie.net/2008/04/09/php-and-regex-how-to-replace-or-remove-a-repeating-character/
What you accomplished in your article is to remove duplicates but not to make them unique. For example: “aabbccaaaaddee” will become “abcade“. What I did is making them unique.
Thanks for your comment… because of it I edited a bit the article to make it more clear about its purpose.
Now that I further understand what you are looking for, I have taken on the challenge of trying to satisfy your needs.
Hopefully you will find this helpful:
http://www.ilovebonnie.net/2008/04/10/php-and-regex-replacing-repeating-characters-with-single-characters-in-a-string/
I want to mention again that “the beauty of using regular expressions is this: a lot of steps that are needed to accomplish some string formating/parsing can be done in one step using RegExp. But if there are the same amount of steps it will be faster not to use RegExp.“
Hey, just thought I’d let you know that I posted a better (php) solution at the other blog post.
http://www.ilovebonnie.net/2008/04/10/php-and-regex-replacing-repeating-characters-with-single-characters-in-a-string/
Here’s the same thing in AS3 (I’m quite terrible at AS3, so I didn’t think I’d have any luck figuring it out)
var myPattern:RegExp = /(.)\1+/gi;var str:String = "aaabbbcccddeeff";
trace(str.replace(myPattern, '$1'));
So what I needed is a string like “aabbccaaaaaddee” to be transformed to “abcde” (please note that there are two groups of “a“s in the first string and only one “a” in the resulting group).
Using “aabbccaaaaaddee” in your regular expression will give us the result “abcade” which is different from “abcde” (note the underlined letters). I need unique chars in the resulting string.
I tried with regular expression but there is no easy way (one step).
Thanks also for benchmarks. Great job.
Ah, terribly sorry about the misunderstanding. I really should read better before making a fool of myself.
Anyway, I came up with this little gem that’s a play off my previous code.
function removeDuplicates(string:String):String {return string.split('').sort().join('').replace(/(.)\1+/gi,'$1');
}
Benchmark on 10,000 runs in AS3
Yours from the post above: 1.0310000000000024 seconds
Mine from this comment: 0.48499999999999943 seconds
Once again, apologies for the misunderstanding and hopefully I didn’t mess it up again.
This should help.
Worked for me.
[…] In my previous article TLP has commented and created a better method. You can see his post here. […]
I’m not very familiar with actionscript, I stumbled upon your site while looking for a reminder on the regex syntax for look-behind in vim and was just a bit fascinated by this problem. I’m just curious, is there a way to transpose an AS array with a native function, so that the values become keys (like in a hash table / associative array)? I assume that in AS like in most other languages, array keys are unique. If it is possible maybe the language native constructs could do these operations faster :
1- split the string in an array
2- transpose the array (which should automatically eliminate duplicate keys).
3- gather all the keys and you have your unique values.
Based on the same concept, if you can’t transpose the array, you could just do a single loop through it and assign its values as keys and values to another array:
(reminder i don’t know AS, this code is based on what i’ve seen above, try to decipher the logic)
var firstArray:Array = thestring.split('');
var secondArray:Array = new Array();
firstArray.forEach(
function (){
secondArray[item] = item;
}
);
Reorder the second array after the operation, since it’s shorter the reordering operation is more efficient.
There’s no guarantee that the whole thing will be faster, if you have the time to benchmark it, maybe it’s worth a shot. Off I go.