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Remove duplicate array elements

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Mar 24.2010

After sorting an array, is this the best way to [B]Remove duplicate array elements?[/B]

[code=html]<SCRIPT type=”text/javascript”>
var a=[‘a’,’a’,’b’,’c’,’c’,’d’,’d’,’d’,’t’,’y’,’y’,’j’,’j’]
document.write(a+’ <B>’+a.length+'</b><p>’)
i=0;while(i<a.length){if(a[i]==a[i+1]){a.splice(i,1);i–} i++}
document.write(a+’ <B>’+a.length+'</b>’)
</SCRIPT>[/code]

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JavaScript

2 Comments(s) ↴

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@rnd_meMar 24.2010 — i don't know about "best", but i use [].filter() and [].lastIndexOf() to run the loop portion in C/JAVA:

[CODE]var a=['a','a','b','c','c','d','d','d','t','y','y','j','j'];
var b=a.filter(function(a,b,c){return c.lastIndexOf(a)===b;});[/CODE]

which yields:
[CODE]["a", "b", "c", "d", "t", "y", "j"][/CODE]


if you have a lot of strings and a lot of repetition, it can be faster (performance-wise) to use an object:

[CODE]var a=['a','a','b','c','c','d','d','d','t','y','y','j','j'];
var ok={}, b=[];
for(var i=0, mx=a.length,o; i<mx; i++){ ok[a[i]]=1; }
for(var i in ok){ b[b.length]=i; }
alert(b);
[/CODE]

this pattern avoids the loop-de-loop of your posted and my first method, but it doesn't work on objects.

that's not deal-breaker because your posted code has the same limitation.

the issue is that ["1", 1] will come out as a single-element array.
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@mrhooMar 24.2010 — // Your method may do for a one off call,

// but you have to sort the array first,

// and you destroy the original array.

// Sometimes you want to preserve the order

// and return a unique array without losing the original


[CODE]Array.prototype.unique= function(){
var L= this.length, i= 0, a= [], tem;
while(i < L){
tem= this[i++];
if(tem!=undefined && a.indexOf(tem)== -1) a[a.length]= tem;
}
return a;
}[/CODE]

// Most browsers have an array indexOf method,

// but you need to add it for IE:

[CODE]Array.prototype.indexOf= [].indexOf ||
function(what, index){
index= index || 0;
var L= this.length;
while(index< L){
if(this[index]=== what) return index;
++index;
}
return -1;
}[/CODE]
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