comp.lang.idl-pvwave archive: archive » Saving for loop values into arrays without know the final size of array

Home » Public Forums » archive » Saving for loop values into arrays without know the final size of array

Show: Today's Messages :: Show Polls :: Message Navigator
E-mail to friend

Re: Saving for loop values into arrays without know the final size of array [message #89156 is a reply to message #89154]

Tue, 29 July 2014 12:58

Russell Ryan
Messages: 122
Registered: May 2012

Senior Member

On Tuesday, July 29, 2014 3:24:15 PM UTC-4, sylveste...@gmail.com wrote:
> I am dealing with a large data set and a for-loop with some if statements involved. thus I do not know what the final size of the for-loop will be and cannot declare the array dimensions beforehand which allows you to save your for-loop answers into an array. Does anyone know of a suggestion about how to work around this?

Mike is right, if you have list, you should use list. However, this is will *NOT* work on IDL <7 and might be a problem for you (say if you distribute the code). If you want to use the "old school" way, then it's something like this.

You'll need to swap the for-loop for a while-loop and grow your arrays by concatenation. Suppose your array is called "arr" and you want it to be a floating point, then your code will look something like this:

arr=[0.0]
i=0L ;init the counter
okay =1b ;start the loop
while okay do begin
if i eq 0 then begin
arr(0)=FIRST_ELEMENT_OF_ARRAY
endif else begin
arr=[arr,ALL_OTHER_ELEMENTS_OF_ARRAY]
endelse
okay = SOME_TESTING_LOGIC_THAT_ONLY_YOU_KNOW
endwhile

This will work. You'll need to fill in the values of the array and stop condition, but we'd need to know more about your program to help. This is the simplest case and will work, however this can be made to be better in a great number of ways. First thing to do is change the line:

arr=[arr,XXXXX]

to something like

arr=[temporary(arr),XXXX]

this will save you memory and execute a tick faster (or always seems to).

Also, this is concatenation, which is horrifically slow in IDL, especially as the arrays get large. So, you're better off to concatenate as few times as possible. Instead of going through the relevant stuff, I'll point you to The Masters:

http://www.idlcoyote.com/code_tips/nullarray.html

Here, David Fanning details a discussion from JD Smith.

good luck...

Russell

Report message to a moderator

[Message index]

		Saving for loop values into arrays without know the final size of array By: sylvestergreene51 on Tue, 29 July 2014 12:24
		Re: Saving for loop values into arrays without know the final size of array By: Michael Galloy on Tue, 29 July 2014 12:35
		Re: Saving for loop values into arrays without know the final size of array By: Russell Ryan on Tue, 29 July 2014 12:58
		Re: Saving for loop values into arrays without know the final size of array By: gpeterso%ucsc.edu on Tue, 29 July 2014 13:56
		Re: Saving for loop values into arrays without know the final size of array By: Michael Galloy on Tue, 29 July 2014 14:31
		Re: Saving for loop values into arrays without know the final size of array By: sylvestergreene51 on Tue, 29 July 2014 17:17
		Re: Saving for loop values into arrays without know the final size of array By: Michael Galloy on Tue, 29 July 2014 22:44

Previous Topic:	Automatically generating IDL bindings
Next Topic:	[ANN] MIDLE - Almost an Alternative to EXECUTE

-=] Back to Top [=-

[ Syndicate this forum (XML) ] [

] [

]

Current Time: Wed Oct 08 15:27:38 PDT 2025

Total time taken to generate the page: 0.00360 seconds