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Re: Build 2D array from loops [message #92744 is a reply to message #92743]

Mon, 22 February 2016 06:30

greg.addr
Messages: 160
Registered: May 2007

Senior Member

On Monday, February 22, 2016 at 2:08:39 PM UTC+1, Matt G wrote:
> Hi, new to IDL so please forgive if very simple request.
>
> I'm trying to build an array where the values stored are in two columns: one with the values of i in my FOR loop, and the other the output of that FOR loop. To make it more complicated, within my FOR loop is an IF condition that skips over bad data.
>
> How do I structure this code so that the array is built from the output of my loops?
>
> Cheers

It's often possible to work without loops in IDL. I'd do it something like this:

IDL> i=indgen(10)
IDL> a=i^2 ;replace with your expression
IDL> b=transpose([[i],[a]]) ;combine into two column array
IDL> b
0 0
1 1
2 4
3 9
4 16
5 25
6 36
7 49
8 64
9 81

Use the where() function to filter out your bad values, e.g.

IDL> q=where(a lt 50) ;keep only values where a<50
IDL> b[*,q]
0 0
1 1
2 4
3 9
4 16
5 25
6 36
7 49

cheers,
Greg

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[Message index]

		Build 2D array from loops By: Matt G on Mon, 22 February 2016 05:08
		Re: Build 2D array from loops By: greg.addr on Mon, 22 February 2016 06:30
		Re: Build 2D array from loops By: Matt G on Thu, 25 February 2016 02:44

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