On Dec 1, 12:00 pm, Yngvar Larsen <larsen.yng...@gmail.com> wrote:
> On Dec 1, 11:37 am, Rob <rj...@le.ac.uk> wrote:
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>> On Nov 30, 8:15 pm, Yngvar Larsen <larsen.yng...@gmail.com> wrote:
>
>>> On Nov 29, 6:53 pm, Heinz Stege <public.215....@arcor.de> wrote:
>
>>>> Hi Rob,
>
>>>> no loop necessary:
>
>>>> array=(randomu(seed,2,6,360,42)-.1)>0. ; sample array
>>>> array=reform(array,n_elements(array)/42,42,/overwrite)
>>>> ii=where(min(array,dim=2) eq 0.,count)
>>>> if count ge 1 then array[ii,*]=0.
>>>> array=reform(array,2,6,360,42,/overwrite)
>
>>> Hm. The /OVERWRITE keyword to REFORM was new to me. Thanks!
>
>>> Silly me. I have somehow always imagined that the compiler was smart
>>> enough to do this (i.e. not copy any data, only alter the internal IDL
>>> descriptor of the ARRAY variable) automatically when input and output
>>> to REFORM is the same variable. But a bit of profiling shows this is
>>> not at all the case. This will be _very_ useful many places in my
>>> operational code...
>
>>> A small comment to the code above: "where(min(array,dim=2) eq 0.)"
>>> obviously only works if array contains only non-negative data. If not,
>>> "where(total(array eq 0, 2) gt 0)" will do the trick also for floating
>>> point data containing negative numbers, with more or less the same
>>> performance.
>
>>> --
>>> Yngvar
>
>> Thanks, that explains why a few results were coming out slightly
>> differently as there are a few negative values.
>
>> Also, the code fails when the final column only has 1 element in it.
>
>> IDL> help, array
>> ARRAY DOUBLE = Array[4320, 1]
>> IDL> help, total(array eq 0, 2)
>> % TOTAL: For input argument <BYTE Array[4320]>, Dimension must be
>> 1.
>
> If the final column has only 1 element, the operation is not necessary
> at all since all elements are already 0 :)
>
> IDL sometimes behaves rather idiotic with singleton dimensions:
>
> IDL> help, fltarr(4320, 1)
> <Expression> FLOAT = Array[4320]
>
> This is a problem when arrays are expected to be 2D, and suddenly are
> automatically 1D. You can avoid it by adding an explicit REFORM
> statement at the appropriate place in the code:
>
> ;; Force ARRAY to be 2D always
> if (size(array, /n_dimensions) eq 1) then $
> array = reform(array, n_elements(array), 1, /overwrite)
>
> --
> Yngvar
I'm not sure if that's the solution as the array was already 2D:
>> IDL> help, array
>> ARRAY DOUBLE = Array[4320, 1]
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