| Re: Array indexing problem [message #37848] |
Thu, 29 January 2004 15:21 |
kashyap
Messages: 26
Registered: April 1993
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Junior Member |
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In article <MPG.1a81e83474fc47e19897be@news.frii.com>,
David Fanning <david@dfanning.com> wrote:
> Michael Wallace writes:
>
> Maybe we can hear from someone who uses it.
>
> Cheers,
>
> David
I use this feature quite a lot, for instance, to
define an array of a different size using a set
of indices where said indices may overflow (happens
all the time), and all I may want at these overflow
points is some default value.
Example: suppose there is an array of element
abundances (say ABUND, with size 30). And a
set of indices indicating the atomic number
(say Z, of size 10386). I want to make a new
array (AZ, of size 10386) which contains the
abundances for each of the Z[i]. Now further
suppose that in some places Z may be 0 or -1,
and for which I simply want to set the abundance
to 1. There are no doubt other ways of doing
this, but AZ=ABUND[Z-1] works fast, transparently,
AND stays readable.
Vinay
--
____________________________________________________________ __________________
kashyap@head-cfa.harvard.edu 617 495 7173 [CfA/P-143] 617 496 7173 [F]
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| Re: Array indexing problem [message #37851 is a reply to message #37848] |
Thu, 29 January 2004 09:58  |
David Fanning
Messages: 11724
Registered: August 2001
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Senior Member |
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Roy writes:
> Thank you for responding so quickly. Compile_opt STRICTARRSUBS works
> for IDL 6.0 but I have to use 5.1. Is there a way to add in a compile
> function, or some else that will look for this error in the original
> code? I don't want to add an error handler, which David suggested.
> The original code can not be altered.
I think this request falls into the general category of wanting
to have your cake and eat it too. :-)
Cheers,
David
--
David W. Fanning, Ph.D.
Fanning Software Consulting, Inc.
Phone: 970-221-0438, E-mail: david@dfanning.com
Coyote's Guide to IDL Programming: http://www.dfanning.com/
Toll-Free IDL Book Orders: 1-888-461-0155
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| Re: Array indexing problem [message #37852 is a reply to message #37851] |
Thu, 29 January 2004 09:43 |
Liam Gumley
Messages: 473
Registered: November 1994
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Senior Member |
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I think your options are
(1) Modify the code
or
(2) Use IDL 6.0
Perhaps you could show us the original code?
"Roy" <roberson_1@yahoo.com> wrote in message
news:c0a9aee5.0401290903.154044d3@posting.google.com...
> Thank you for responding so quickly. Compile_opt STRICTARRSUBS works
> for IDL 6.0 but I have to use 5.1. Is there a way to add in a compile
> function, or some else that will look for this error in the original
> code? I don't want to add an error handler, which David suggested.
> The original code can not be altered.
>
> Roy
>
> "Liam Gumley" <pip_book@mailinator.com> wrote in message
news:<bv9c35$lqf$1@news.doit.wisc.edu>...
>> "Roy" <roberson_1@yahoo.com> wrote in message
>> news:c0a9aee5.0401281200.400888f1@posting.google.com...
>>> Is there any existing code that will catch the below IDL simple
>>> example? Input a and b must be an array.
>>>
>>> Input is an array:
>>> IDL> b=[4]
>>> IDL> a=[0,1,2]
>>> IDL> print,a[b]
>>> 2
>>> This should give me an error.
>>
>> This is how array subscripting works in IDL, when the subscript is an
array.
>> To quote the IDL Manual "Building IDL Applications", Chapter 5, "Using
>> Arrays as Subscripts":
>>
>> "If an element of the subscript array is less than or equal to zero, the
>> first element of the subscripted variable is selected. If an element of
the
>> subscript is greater than or equal to the last subscript in the
subscripted
>> variable (N, above), the last element is selected."
>>
>> If the subscript variable has just one elements, then you can do this
>> instead
>>
>> IDL> print, a[b[0]]
>> % Attempt to subscript A with <LONG ( 4)> is out of range.
>> % Execution halted at: $MAIN$
>>
>> since b[0] is a scalar. You can do this even if b is a scalar.
>>
>> Cheers,
>> Liam.
>> Practical IDL Programming
>> http://www.gumley.com/
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| Re: Array indexing problem [message #37853 is a reply to message #37852] |
Thu, 29 January 2004 09:03 |
roberson_1
Messages: 10
Registered: November 2003
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Junior Member |
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Thank you for responding so quickly. Compile_opt STRICTARRSUBS works
for IDL 6.0 but I have to use 5.1. Is there a way to add in a compile
function, or some else that will look for this error in the original
code? I don't want to add an error handler, which David suggested.
The original code can not be altered.
Roy
"Liam Gumley" <pip_book@mailinator.com> wrote in message news:<bv9c35$lqf$1@news.doit.wisc.edu>...
> "Roy" <roberson_1@yahoo.com> wrote in message
> news:c0a9aee5.0401281200.400888f1@posting.google.com...
>> Is there any existing code that will catch the below IDL simple
>> example? Input a and b must be an array.
>>
>> Input is an array:
>> IDL> b=[4]
>> IDL> a=[0,1,2]
>> IDL> print,a[b]
>> 2
>> This should give me an error.
>
> This is how array subscripting works in IDL, when the subscript is an array.
> To quote the IDL Manual "Building IDL Applications", Chapter 5, "Using
> Arrays as Subscripts":
>
> "If an element of the subscript array is less than or equal to zero, the
> first element of the subscripted variable is selected. If an element of the
> subscript is greater than or equal to the last subscript in the subscripted
> variable (N, above), the last element is selected."
>
> If the subscript variable has just one elements, then you can do this
> instead
>
> IDL> print, a[b[0]]
> % Attempt to subscript A with <LONG ( 4)> is out of range.
> % Execution halted at: $MAIN$
>
> since b[0] is a scalar. You can do this even if b is a scalar.
>
> Cheers,
> Liam.
> Practical IDL Programming
> http://www.gumley.com/
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| Re: Array indexing problem [message #37858 is a reply to message #37853] |
Wed, 28 January 2004 13:43 |
hunter
Messages: 9
Registered: June 2003
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Junior Member |
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You can also turn off this feature if it offends.
compile_opt strictarrsubs
And you will get an error for the example you mentioned above.
Eli
"David Fanning" <david@dfanning.com> wrote in message
news:MPG.1a81d8b95abba27f9897bd@news.frii.com...
> Roy writes:
>
>> Is there any existing code that will catch the below IDL simple
>> example? Input a and b must be an array.
>>
>>
>> Input is an array:
>> IDL> b=[4]
>> IDL> a=[0,1,2]
>> IDL> print,a[b]
>> 2
>> This should give me an error.
>
> Alas, you have run into a little known, but enormously
> appreciated, little feature of IDL. (I'm sure it is
> explained in the manuals somewhere. :-)
>
> Maybe something like this for an error handler:
>
> IF Total(b GT ((N_Elements(a) -1)) GT 0 THEN $
> Message, 'B indices exceed bounds of A'
>
> Cheers,
>
> David
> --
> David W. Fanning, Ph.D.
> Fanning Software Consulting, Inc.
> Phone: 970-221-0438, E-mail: david@dfanning.com
> Coyote's Guide to IDL Programming: http://www.dfanning.com/
> Toll-Free IDL Book Orders: 1-888-461-0155
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| Re: Array indexing problem [message #37861 is a reply to message #37858] |
Wed, 28 January 2004 16:55 |
Mark Hadfield
Messages: 783
Registered: May 1995
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Senior Member |
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David Fanning wrote:
> Maybe we can hear from someone who uses it.
Not me, but I would like to point out that this "desirable" behaviour
can be eliminated in version 6.0 by adding the following declaration to
your code
compile_opt STRICTARRSUBS
I have this, along with DEFINT32, STRICTARR & LOGICAL_PREDICATE in my
start-up file and all recently-edited routines.
This done, Roy's example gives me
% Array used to subscript array contains out of range subscript: A.
--
Mark Hadfield "Ka puwaha te tai nei, Hoea tatou"
m.hadfield@niwa.co.nz
National Institute for Water and Atmospheric Research (NIWA)
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| Re: Array indexing problem [message #37862 is a reply to message #37858] |
Wed, 28 January 2004 14:40 |
David Fanning
Messages: 11724
Registered: August 2001
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Senior Member |
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Michael Wallace writes:
> Could you elaborate on the "enormously appreciated" part of your
> statement? Maybe I'm not thinking in the "IDL Way," but I would not
> have expected the result IDL gives. It may very well be explained in
> the manuals, but why is such a "feature" "enormously appreciated?"
I can't remember. :-)
I do remember the first time I pointed this "bug"
out on the IDL newsgroup years and years ago and
how mortified I was when Ray Sterner publicly
pointed out what a GREAT and USEFUL thing it was.
(In those days Ray was the word on the IDL newsgroup.)
In fact, it may have been this fiasco that caused
Dave Stern to send around that memo forbidding RSI
employees from posting on the newsgroup.
Odd that in 17 years of programming I've never run
across the need for this. But there you go. An historical
perspective.
Maybe we can hear from someone who uses it.
Cheers,
David
P.S. Let's just say I've never bothered to sing much
either after my 7th grade music teacher in a fit of pique
told me I had a "two note range". Funny what power those
formative experiences have on you. :-)
--
David W. Fanning, Ph.D.
Fanning Software Consulting, Inc.
Phone: 970-221-0438, E-mail: david@dfanning.com
Coyote's Guide to IDL Programming: http://www.dfanning.com/
Toll-Free IDL Book Orders: 1-888-461-0155
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| Re: Array indexing problem [message #37863 is a reply to message #37858] |
Wed, 28 January 2004 14:28 |
Paul Van Delst[1]
Messages: 1157
Registered: April 2002
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Senior Member |
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Michael Wallace wrote:
>
>>> Is there any existing code that will catch the below IDL simple
>>> example? Input a and b must be an array.
>>>
>>>
>>> Input is an array:
>>> IDL> b=[4]
>>> IDL> a=[0,1,2]
>>> IDL> print,a[b]
>>> 2
>>> This should give me an error.
>>
>>
>> Alas, you have run into a little known, but enormously
>> appreciated, little feature of IDL. (I'm sure it is
>> explained in the manuals somewhere. :-)
>
> Could you elaborate on the "enormously appreciated" part of your
> statement? Maybe I'm not thinking in the "IDL Way," but I would not
> have expected the result IDL gives. It may very well be explained in
> the manuals, but why is such a "feature" "enormously appreciated?"
After reading Liam's explanation, I would _still_ like elaboration on why this is
"enormously appreciated"! :o) Seems a bizarre feature to me..... but at least it's
documented.
paulv
--
Paul van Delst
CIMSS @ NOAA/NCEP/EMC
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| Re: Array indexing problem [message #37865 is a reply to message #37858] |
Wed, 28 January 2004 14:23 |
Michael Wallace
Messages: 409
Registered: December 2003
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Senior Member |
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>> Is there any existing code that will catch the below IDL simple
>> example? Input a and b must be an array.
>>
>>
>> Input is an array:
>> IDL> b=[4]
>> IDL> a=[0,1,2]
>> IDL> print,a[b]
>> 2
>> This should give me an error.
>
>
> Alas, you have run into a little known, but enormously
> appreciated, little feature of IDL. (I'm sure it is
> explained in the manuals somewhere. :-)
Could you elaborate on the "enormously appreciated" part of your
statement? Maybe I'm not thinking in the "IDL Way," but I would not
have expected the result IDL gives. It may very well be explained in
the manuals, but why is such a "feature" "enormously appreciated?"
Mike
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| Re: Array indexing problem [message #37866 is a reply to message #37858] |
Wed, 28 January 2004 14:11 |
Liam Gumley
Messages: 473
Registered: November 1994
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Senior Member |
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"Roy" <roberson_1@yahoo.com> wrote in message
news:c0a9aee5.0401281200.400888f1@posting.google.com...
> Is there any existing code that will catch the below IDL simple
> example? Input a and b must be an array.
>
> Input is an array:
> IDL> b=[4]
> IDL> a=[0,1,2]
> IDL> print,a[b]
> 2
> This should give me an error.
This is how array subscripting works in IDL, when the subscript is an array.
To quote the IDL Manual "Building IDL Applications", Chapter 5, "Using
Arrays as Subscripts":
"If an element of the subscript array is less than or equal to zero, the
first element of the subscripted variable is selected. If an element of the
subscript is greater than or equal to the last subscript in the subscripted
variable (N, above), the last element is selected."
If the subscript variable has just one elements, then you can do this
instead
IDL> print, a[b[0]]
% Attempt to subscript A with <LONG ( 4)> is out of range.
% Execution halted at: $MAIN$
since b[0] is a scalar. You can do this even if b is a scalar.
Cheers,
Liam.
Practical IDL Programming
http://www.gumley.com/
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| Re: Array indexing problem [message #37867 is a reply to message #37858] |
Wed, 28 January 2004 13:34 |
David Fanning
Messages: 11724
Registered: August 2001
|
Senior Member |
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Roy writes:
> Is there any existing code that will catch the below IDL simple
> example? Input a and b must be an array.
>
>
> Input is an array:
> IDL> b=[4]
> IDL> a=[0,1,2]
> IDL> print,a[b]
> 2
> This should give me an error.
Alas, you have run into a little known, but enormously
appreciated, little feature of IDL. (I'm sure it is
explained in the manuals somewhere. :-)
Maybe something like this for an error handler:
IF Total(b GT ((N_Elements(a) -1)) GT 0 THEN $
Message, 'B indices exceed bounds of A'
Cheers,
David
--
David W. Fanning, Ph.D.
Fanning Software Consulting, Inc.
Phone: 970-221-0438, E-mail: david@dfanning.com
Coyote's Guide to IDL Programming: http://www.dfanning.com/
Toll-Free IDL Book Orders: 1-888-461-0155
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