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Re: Clever Where() test [message #4376 is a reply to message #4370]

Thu, 25 May 1995 00:00

thompson
Messages: 584
Registered: August 1991

Senior Member

afl@cdc.noaa.gov (Andy Loughe) writes:

> In article <moleD93CEG.79n@netcom.com>, mole@netcom.com (Aaron Birenboim) writes:
> |> Is there a clever way to test for null return (-1) from WHERE???
> |>
> |> I'm doing stuff like :
> |>
> |> i = WHERE(x GT 0.0)
> |> s = SIZE(i)
> |> IF s(0) EQ 0 THEN BEGIN
> |> IF i GE 0 THEN BEGIN
> |> ; do something with x(i)
> |> ENDIF
> |> ENDIF ELSE BEGIN
> |> ; do something with the multiple elements x(i)
> |> ENDIF
> |>
> |> Is there a more clever way to handle this? Especially since the
> |> "do something...." code is often the same weather i is scalar or vector.
> |>
> |> I wish that "IF i eq -1 THEN..." wouldnt crash for vector i's!!!
> |> --

> How about this?

> i = WHERE( x GT 0.0, count)
> IF ( count gt 0 ) then 'do something with the x's

> The count is very handy indeed. You could also build a
> loop from 0, count-1 if you needed to.

For that matter, one could also do

i = WHERE(x GT 0.0)
IF i(0) NE -1 THEN 'do something with the x's

although I also prefer using the optional count parameter. On the other hand,
if all one cared about was whether and matches were found, and didn't care
where they are, then one could do something like

IF (WHERE(x GT 0.0))(0) NE -1 THEN PRINT, 'At least one is > 0.0'

One can always reference a variable with (0), even if it's a scalar.

Bill Thompson

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[Message index]

		Re: Clever Where() test By: steinhh on Fri, 26 May 1995 00:00
		Re: Clever Where() test By: thompson on Thu, 25 May 1995 00:00
		Re: Clever Where() test By: Paul Probert on Thu, 25 May 1995 00:00
		Re: Clever Where() test By: thompson on Thu, 25 May 1995 00:00
		Re: Clever Where() test By: bertin on Thu, 25 May 1995 00:00
		Re: Clever Where() test By: afl on Wed, 24 May 1995 00:00
		Re: Clever Where() test By: offenbrg on Tue, 30 May 1995 00:00
		Re: Clever Where() test By: thompson on Tue, 30 May 1995 00:00

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