Cheers Jean, that code of yours runs well.
However, I decided to switch back to my original code with the for
loop. This was because the time taken to sort increases significantly
with the number of elements to be sorted. In your approach, you are
sorting the entire array, and then working out what elements are in
each row.
My original code (with the loops) runs faster (for me anyway), because
each sort operation is sorting a smaller subset of the numners, and so
is quicker.
That is, unless somebody can proof me wrong :-p
Humphrey
Jean H. wrote:
> a = [[4,2,0,5],[9,0,1,5],[0,4,2,1],[1,2,3,4]]
> b = sort(a) ;sort the whole array
>
> sizeX = 4 ;(use DIM instead)
> sizeY = 4
> nbElements = n_elements(a)
>
> c = b/sizeX ;tells you, for each element of b, which line of A the
> ;index correspond to
>
> useless = histogram(c, reverse_indices = ri)
> ;get the reverse indices of the histogram. It tells you, for each line
> of a (print useless, you will get 4 4 4 4), the indices of b that
> correspond to it.
>
> ;get the sorted indices, resorted by lines. You have, for sure, 4 bin
> here, so the first indice of b is located at ri[5].
> d = b[ri[sizeX+1:sizeX+nbElements]]
>
> minus = indgen(sizeY) * sizeX
> minusBIG = transpose(rebin(minus,sizeX,sizeY))
> ;you want the indices on each line and not on the whole array (if that's
> what you want, d is fine for you then)
>
> result = reform(d-minusBIG, sizeX,sizeY)
>
>
> IDL> print, result
> 2 1 0 3
> 1 2 3 0
> 0 3 2 1
> 0 1 2 3
>
>
> I suggest you to learn to use the histogram... it's wonderful what you
> can do with it!
>
> Jean
>
>
> humphreymurray@gmail.com wrote:
>> Hi,
>>
>> In IDL, is there a way to independly sort the columns of a 2d matrix
>> without looping through and sorting each row individually?
>>
>> Currenly I'm using:
>>
>> for x = long(0), x_size - 1 do begin
>> sorted_indexs[0,x] = sort(matrix[*,x])
>> endfor
>>
>> For example, if the matrix contained the following values:
>>
>> 4 2 0 5
>> 9 0 1 5
>> 0 4 2 1
>> 1 2 3 4
>>
>> I want the result matrix to contain index's like:
>>
>> 2 1 0 3
>> 1 2 3 0
>> 0 3 2 1
>> 0 1 2 3
>>
>> Here, each column is sorted as if it's an independant vector.
>>
>> Cheers.
>>
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