| keyword params in HISTOGRAM [message #7546] |
Wed, 20 November 1996 00:00  |
Mark Fardal
Messages: 51
Registered: October 1995
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Member |
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Hi,
I'm sure this is a stupid question, but I can't figure it out.
Normally when you pass keyword parameters, you can pass something
that's undefined, right? As in this example
pro junk1, a, test=test
help,test,t
;junk2, a, test=test ; either one of
junk2, a, test=t ; these works
return
end
pro junk2, a, test=test
a = 3.
return
end
IDL> junk1, a
TEST UNDEFINED = <Undefined>
T UNDEFINED = <Undefined>
IDL>
However, when I try to pass HISTOGRAM a keyword parameter that's
undefined, I get an error message. The routine here is just a
wrapper function for HISTOGRAM, so I want to pass a number of
keyword parameters through to it.
function histomake, array, binsize=binsize, xpoints=xpoints, $
input=input, min=min, max=max, omin=omin, omax=omax, reverse=reverse
[...stuff deleted...]
n = histogram(array, binsize=binsize, min=min, max=max, $
omin=omin, omax=omax, reverse=reverse)
[...stuff deleted...]
return
end
IDL> h = histomake(array, bins=10, xpoints=xpoints)
% HISTOGRAM: Variable is undefined: MAX.
% Execution halted at: HISTOMAKE 52
/users1/casa/fardal/comp/idl/histomake.pro
% $MAIN$
Why is the behavior different here?
Thanks,
Mark
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| Re: keyword params in HISTOGRAM [message #7606 is a reply to message #7546] |
Tue, 03 December 1996 00:00  |
thompson
Messages: 584
Registered: August 1991
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Senior Member |
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Mark Fardal wrote:
>
> Hi,
>
> I'm sure this is a stupid question, but I can't figure it out.
> Normally when you pass keyword parameters, you can pass something
> that's undefined, right? As in this example
>
(rest deleted)
Although the example you give isn't optimal, it is correct that you can pass
undefined keywords to procedures. This is because inside procedures you can
check to see if keywords are passed with either the N_ELEMENTS function or
KEYWORD_SET. Thus, passing an undefined keyword is equivalent to not passing
it at all, which is a useful thing IMHO. Unfortunately, this doesn't work with
built-in IDL routines, which I find a very inconvenient and silly restriction.
Bill Thompson
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| Re: keyword params in HISTOGRAM [message #7609 is a reply to message #7546] |
Tue, 03 December 1996 00:00 |
Robert Moss
Messages: 74
Registered: February 1996
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Member |
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Mark Fardal wrote:
>
> Hi,
>
> I'm sure this is a stupid question, but I can't figure it out.
> Normally when you pass keyword parameters, you can pass something
> that's undefined, right? As in this example
>
> pro junk1, a, test=test
> help,test,t
> ;junk2, a, test=test ; either one of
> junk2, a, test=t ; these works
> return
> end
>
> pro junk2, a, test=test
>
> a = 3.
> return
> end
>
> IDL> junk1, a
> TEST UNDEFINED = <Undefined>
> T UNDEFINED = <Undefined>
> IDL>
>
> However, when I try to pass HISTOGRAM a keyword parameter that's
> undefined, I get an error message. The routine here is just a
> wrapper function for HISTOGRAM, so I want to pass a number of
> keyword parameters through to it.
>
> function histomake, array, binsize=binsize, xpoints=xpoints, $
> input=input, min=min, max=max, omin=omin, omax=omax, reverse=reverse
> [...stuff deleted...]
>
> n = histogram(array, binsize=binsize, min=min, max=max, $
> omin=omin, omax=omax, reverse=reverse)
>
> [...stuff deleted...]
> return
> end
>
> IDL> h = histomake(array, bins=10, xpoints=xpoints)
> % HISTOGRAM: Variable is undefined: MAX.
> % Execution halted at: HISTOMAKE 52
> /users1/casa/fardal/comp/idl/histomake.pro
> % $MAIN$
>
> Why is the behavior different here?
>
> Thanks,
> Mark
Your junk example "works" because you are not trying to actually do
anything with the test variable in the junk2 routine... hence no error
occurs.
The HISTOGRAM routine _is_ trying to do something with its keywords, so
you get an error. I see two reasonable solutions:
1) If you are not using the min, max, etc keywords in the histomake
function itself, rather than making them explicit keywords, use keyword
inheritance ( the _EXTRA keyword) to pass them to HISTOGRAM. (See EXTRA
in the online help).
2) Use the CALL_FUNCTION (faster) or EXECUTE (slower) method to call
HISTOGRAM inside your makeohist function so that it is called with only
the relevant and proper keywords.
At a guess, I'd say that solution 1) is the way to go in general...
keyword inheritance is a Good Thing.
--
Robert M. Moss, Ph.D. - mossrm@texaco.com - FAX (713)954-6911
------------------------------------------------------------ -----
This does not necessarily reflect the opinions of Texaco Inc.
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