Assigning between arrays by value

[John Geddes]

Any neat way to copy a snapshot of one array to another?

A normal assignment results in the second array pointing to the first,
with changes to either array affecting both.

As a trivial example:

var a=new Array();
a[0]="zero";
var b=a;
b[1]="one";
alert("a="+a.jo in("*")+String. fromCharCode(10 )+"b="+b.join(" *"));

.... this results in a and b being identical two-element arrays.

Is there any easy way to set array (b) to be a copy of (a) BY VALUE -
ie using the contents of (a) as they were at the moment of assignment,
but leaving the two arrays separate so that subsequent changes to one
array does not affect the other?

John Geddes
England

[Lasse Reichstein Nielsen]

Re: Assigning between arrays by value

john@starmarkas sociates.co.uk (John Geddes) writes:
[color=blue]
> Any neat way to copy a snapshot of one array to another?[/color]

There are some.
[color=blue]
> A normal assignment results in the second array pointing to the first,
> with changes to either array affecting both.[/color]

You can do it manually:
---
function cloneArray(arr) {
var newArr = new Array();
for (var i=0;i<arr.lengt h;i++) {
newArr[i]=arr[i];
}
return newArr;
}
---
Or you can use one of the methods that work on parts of the array:

var newArr = arr.slice(0,arr .length);


/L
--
Lasse Reichstein Nielsen - lrn@hotpop.com
Art D'HTML: <URL:http://www.infimum.dk/HTML/randomArtSplit. html>
'Faith without judgement merely degrades the spirit divine.'

[Dr John Stockton]

Re: Assigning between arrays by value

JRS: In article <708430f3.03092 20622.327c20bd@ posting.google. com>, seen
in news:comp.lang. javascript, John Geddes <john@starmarka ssociates.co.uk[color=blue]
> posted at Mon, 22 Sep 2003 07:22:35 :-[/color]
[color=blue]
>Any neat way to copy a snapshot of one array to another?[/color]

A = [1, 2, 3]
C = [].concat(A)
C[1] = 4
x = [A, ' ', C] ; alert(x) // 1,2,3, ,1,4,3

But note

A = [1, 2, [5,6,7]]
C = [].concat(A)
C[1] = 4 ; C[2][1] = 9 // 1,2,5,9,7, ,1,4,5,9,7

though

A = [1, 2, [5,6,7]]
C = [].concat(A)
C[1] = 4 ; C[2] = 8 // 1,2,5,6,7, ,1,4,8

The "top level" of A is copied, but not lower levels.

--
© John Stockton, Surrey, UK. ?@merlyn.demon. co.uk Turnpike v4.00 IE 4 ©
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[asdf asdf]

Re: Assigning between arrays by value

Can you alter the Array prototype and add a clone or deepclone method?
They could then handle inner arrays however you wanted.