| Re: negative indices, am I missing something here? [message #81956] |
Tue, 06 November 2012 04:20 |
d.rowenhorst@gmail.co
Messages: 10
Registered: August 2008
|
Junior Member |
|
|
Many thanks. I'll categorize this as a bugture (a bug inducing feature).
On Friday, November 2, 2012 6:36:08 PM UTC-4, David Fanning wrote:
> Michael Galloy writes:
>
>
>
>> Might be a good idea to use
>
>>
>
>> compile_opt strictarrsubs
>
>>
>
>> to catch these cases.
>
>
>
> Maybe somebody can write a script to paw through 25 years
>
> of archived programs. :-)
>
>
>
> Cheers,
>
>
>
> David
>
>
>
>
>
> --
>
> David Fanning, Ph.D.
>
> Fanning Software Consulting, Inc.
>
> Coyote's Guide to IDL Programming: http://www.dfanning.com/
>
> Sepore ma de ni thue. ("Perhaps thos speakest truth.")
|
|
|
|
|
|
| Re: negative indices, am I missing something here? [message #81987 is a reply to message #81986] |
Fri, 02 November 2012 15:26  |
Michael Galloy
Messages: 1114
Registered: April 2006
|
Senior Member |
|
|
On 11/2/12 3:53 PM, David Fanning wrote:
> fawltylanguage@gmail.com writes:
>
>> Array subscripts are always clipped. From IDL help:
>>
>> "If an element of the subscript array is less than or equal to zero, the first element of the subscripted array is selected. ...
>>
>> Note: Because of the confusion between the clipping of array subscripts and the use of negative indices (see the next section), it is best to avoid using code that relies on this clipping behavior."
>
> You can think of it as karmic justice for sins of the past. ;-)
>
> Cheers,
>
> David
>
>
Might be a good idea to use
compile_opt strictarrsubs
to catch these cases.
Mike
--
Michael Galloy
www.michaelgalloy.com
Modern IDL: A Guide to IDL Programming (http://modernidl.idldev.com)
Research Mathematician
Tech-X Corporation
|
|
|
|
| Re: negative indices, am I missing something here? [message #81989 is a reply to message #81987] |
Fri, 02 November 2012 14:53 |
David Fanning
Messages: 11724
Registered: August 2001
|
Senior Member |
|
|
fawltylanguage@gmail.com writes:
> Array subscripts are always clipped. From IDL help:
>
> "If an element of the subscript array is less than or equal to zero, the first element of the subscripted array is selected. ...
>
> Note: Because of the confusion between the clipping of array subscripts and the use of negative indices (see the next section), it is best to avoid using code that relies on this clipping behavior."
You can think of it as karmic justice for sins of the past. ;-)
Cheers,
David
--
David Fanning, Ph.D.
Fanning Software Consulting, Inc.
Coyote's Guide to IDL Programming: http://www.dfanning.com/
Sepore ma de ni thue. ("Perhaps thos speakest truth.")
|
|
|
|
| Re: negative indices, am I missing something here? [message #81990 is a reply to message #81989] |
Fri, 02 November 2012 14:39 |
Lajos Foldy
Messages: 176
Registered: December 2011
|
Senior Member |
|
|
On Friday, November 2, 2012 8:51:56 PM UTC+1, d.rowe...@gmail.com wrote:
> IDL 8 brought negative indices for arrays. Great, love them. However, I am getting strange results.
>
>
>
> IDL> a = indgen(3,5)
>
> IDL> print, a[*,-1]
>
> 12 13 14
>
>
>
> Good, that is what I thought I should get.
>
>
>
> IDL> print, a[*, [3,1,4]]
>
> 9 10 11
>
> 3 4 5
>
> 12 13 14
>
>
>
> Also, this looks right to me.
>
>
>
> So why doesn't this work?
>
> IDL> print, a[*, [3,1,-1]]
>
> 9 10 11
>
> 3 4 5
>
> 0 1 2
>
>
>
> Is this the expected behavior? Or a bug?
>
>
>
> Mac 10.8.2 IDL 8.2.1
Array subscripts are always clipped. From IDL help:
"If an element of the subscript array is less than or equal to zero, the first element of the subscripted array is selected. ...
Note: Because of the confusion between the clipping of array subscripts and the use of negative indices (see the next section), it is best to avoid using code that relies on this clipping behavior."
regards,
Lajos
|
|
|
|
comp.lang.idl-pvwave archive
Members
Search
Help
Login
Home
