Is it better to make a big array with slots not used or redim an array over and over

[rejectpenguin]

So, is it better to keep rediming an array or to just make a huge array with options you wont use?

[martin]

  On 8/17/2009 at 8:51 PM, 'rejectpenguin said:

So, is it better to keep rediming an array or to just make a huge array with options you wont use?

Probably impossible to give a definitive answer, but my preference is to create an array which I think will be big enough to start with, and if I find it needs to be larger then increase it by a reasonable amount so that I don't have to increase it too often. Sometimes you won't know how big an array will need to be so you can't create it at a maximum size anyway.

[Melba23]

rejectpenguin,

One trick I have found useful if you really have no idea how big an array could get is to make the array a reasonable size to begin with and then double it each time it needs to be increased in size. As you may have noticed, ReDims are very slow and can really cause problems in a loop. By using the doubling technique you perform many fewer ReDims and save a lot of time - but you do need to keep a count of where in the array you are. Some snippets to give you an idea of what I mean:

; Declare the array 
Local $asList[10] = [1]

; Then when you want to add to the array

; Increase array count
$asList[0] += 1
; Double array size if too small (fewer ReDim needed)
If UBound($asList) <= $asList[0] + 1 Then ReDim $asList[UBound($asList) * 2]
; Add to list
$asList[$asList[0]] = $value

; And then when you have finished

; If required, remove unused array elements from last ReDim
ReDim $asList[$asList[0] + 1]

This array would increase: 10, 20, 40, 80, 160, 320, 640, 1280, etc - only 7 ReDims needed to get over 1000 elements. If you know you are likely to end up with a really big array, just increase the initial size or use a bigger factor when increasing the size.

M23