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Re: I would like to average the first n columns based on duplicate values of the n+1th column [message #93714 is a reply to message #93699]

Tue, 04 October 2016 05:34

Helder Marchetto
Messages: 520
Registered: November 2011

Senior Member

On Monday, October 3, 2016 at 11:05:31 PM UTC+2, belk...@web.de wrote:
> Hey,
> Can Someone help me solve this problem in IDL:
> "I have a matrix with duplicate numbers in one of the columns. I would like to average the rows with duplicate numbers. For example, I have duplicate values in a matrix A in column 3:
>
> A =
> 1 2 1
> 4 4 2
> 5 4 2
> 4 5 2
> 5 5 3
> 10 3 3
>
>
> B =
> 1 2 1
> 4.3333 4.3333 2.0000
> 7.5000 4.0000 3.0000
>
> where each row is the average values of the duplicate rows of column 3.
>
> Can anyone help?"
>
> found here:
> http://stackoverflow.com/questions/15270019/i-would-like-to- average-the-first-n-columns-based-on-duplicate-values-of-the -n1
>
> Cheers,
> B.R.

Ok, this might not be instructive. But it was fun to look into.
I basically shortened the whole thing into two instructions:

u = [uniq(a[2,*],sort(a[2,*])),n_elements(a[2,*])-1]
for i=0,n_elements(u)-2 do print, [total(reform(a[0:1,lindgen(u[i+1]-u[i]+1,start=u[i])],2,u[i +1]-u[i]+1),2)/float(u[i+1]-u[i]+1),a[2,u[i]]]

This works if a is defined as:
a = [[ 1, 2, 1],$
[ 4, 4, 2],$
[ 5, 4, 2],$
[ 4, 5, 2],$
[ 5, 5, 3],$
[10, 3, 3]]
This is what I get:
2.50000 3.00000 1.00000
4.50000 4.50000 2.00000
7.50000 4.00000 3.00000
Similar to Markus version, but it does not use the where().

Anyway, this was already solved, so it was a just for fun thing to do.

Cheers,
Helder

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[Message index]

		I would like to average the first n columns based on duplicate values of the n+1th column By: belkaraza on Mon, 03 October 2016 14:05
		Re: I would like to average the first n columns based on duplicate values of the n+1th column By: Markus Schmassmann on Tue, 04 October 2016 03:32
		Re: I would like to average the first n columns based on duplicate values of the n+1th column By: belkaraza on Tue, 04 October 2016 04:17
		Re: I would like to average the first n columns based on duplicate values of the n+1th column By: belkaraza on Tue, 04 October 2016 04:23
		Re: I would like to average the first n columns based on duplicate values of the n+1th column By: belkaraza on Tue, 04 October 2016 04:32
		Re: I would like to average the first n columns based on duplicate values of the n+1th column By: Markus Schmassmann on Tue, 04 October 2016 04:35
		Re: I would like to average the first n columns based on duplicate values of the n+1th column By: Helder Marchetto on Tue, 04 October 2016 05:34

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