Re: Philosophy of for loops

[landsman(at)my-deja.com]

 Todd Clements wrote:
> >
> > Hello, again, everyone!
> >
> > I was just wondering what the general concensus of the "IDL Expert
> > Programmers" was on the use of for loops. When I first learned IDL,

A related question is when is it better to write loops as a single line,
and when is it better to use a DO BEGIN construct.   For example,

inarr= randomn(seed, 3, 2048,2048)
outarr = fltarr(2048,2048,/nozero)

(1) for j=0,2047 do for i=0,2047 do outarr[i,j] = median(inarr[*,i,j])

(2) for j=0,2047 do begin
    for i=0,2047 do begin
        outarr[i,j] = median(inarr[*,i,j])
    endfor
    endfor

Form (1) is slightly faster, but the calculation cannot be interrupted
with a Control-C.   Also, it is my impression that the speed difference
is less than it used to be, and that form (2) is now better optimized.

(I also assume that the two FOR loops are unavoidable here, but I would
be delighted to be proved wrong.)

--Wayne Landsman                         landsman@mpb.gsfc.nasa.gov


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