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Re: Build 2D array from loops [message #92754 is a reply to message #92744]

Thu, 25 February 2016 02:44

Matt G
Messages: 4
Registered: February 2016

Junior Member

On Monday, February 22, 2016 at 2:30:18 PM UTC, greg...@googlemail.com wrote:
> 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

Couldn't work out how to avoid a loop completely (it's quite a lengthy process for the data) but managed to sort out my issue from your advice.

Thanks a bunch!
Matt

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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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