Re: idl2matlab translate-o-matic

["David McClain" <dmcclain(at)azstarnet.com>]

I knew that if you thought about it you would begin to understand my
point...

Try this one... Give me a function to return the array result of removing
selected items from an argument array.

Since I can't pass a testing function to that routine (IDL doesn't have
higher order functions), I will accept a routine, for illustrative purposes,
that removes all even values from the array.

Now suppose some joker passes an array containing only even values to that
routine...

- DM

Craig Markwardt <craigmnet@cow.physics.wisc.edu> wrote in message
onya8drxcf.fsf@cow.physics.wisc.edu">news:onya8drxcf.fsf@cow.physics.wisc.edu...
>
> Pavel Romashkin <pavel@netsrv1.cmdl.noaa.gov> writes:
>
> > > What can you say of a language that is purely array oriented, but
> > > cannot comprehend the existence of an empty array?
> >
> > Agreeing with D.F., I so far had no use for an empty array. I
> > understand it is not flexible, but I usually work on data other than
> > nothing.
>
> Forgive him, he knows not what he says.
>
> Empty arrays would be invaluable in both indexing (such as with WHERE)
> and array concatenation.  By invaluable, I mean that it would remove a
> lot of the special casing.  Consider these examples:
>
> ARRAY INDEXING - indexing with where()
>  *With* an empty array:
>    wh = where(array GT thresh, /EMPTY)
>    array(wh) = 0   ;; indexing with empty array has no effect
>  *Without* an empty array
>    wh = where(array GT thresh, count)
>    if count GT 0 then array(wh) = 0
>
> ARRAY CONCATENATION - growing an array
>  *With* an empty array:
>    l = empty_array()
>    for i = 0, 100 do if expression(values) then l = [l, values]
>  *Without* an empty array:
>    for i = 0, 100 do $
>      if expression then $
>         if n_elements(l) EQ 0 then l = [values] else l = [l, values]
>
> As you can see, the "with" code is more simple and easy to read.  The
> "without" (which represents the status quo) has special cases which
> ruin the flow of thought.  For a vectorized language, this is a
> painful burden to bear sometimes.  If you don't believe me, try doing
> the following (apparently simple) problem:
>
>  * given two arrays, A and B: concatenate all but the last two
>    elements of A, with B.  Don't try [A(0:n-3),B], or you will be in a
>    world of hurt.
>
> Craig
>
> --
> --------------------------------------------------------------------------
> Craig B. Markwardt, Ph.D.         EMAIL:    craigmnet@cow.physics.wisc.edu
> Astrophysics, IDL, Finance, Derivatives | Remove "net" for better response
> --------------------------------------------------------------------------