| Re: indexing a structure in a list [message #87477 is a reply to message #87475] |
Wed, 05 February 2014 11:42  |
Helder Marchetto
Messages: 520
Registered: November 2011
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Senior Member |
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On Wednesday, February 5, 2014 7:05:02 PM UTC+1, Mike Galloy wrote:
> On 2/5/14, 10:52 AM, Craig Markwardt wrote:
>
>> On Wednesday, February 5, 2014 11:36:09 AM UTC-5, Helder wrote:
>
>>> Hi,
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>>>
>
>>> I've got the feeling this should work, but for some reason it isn't.
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>>>
>
>>> So here is some code to test the problem with the errors describe in it:
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>>>
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>>>
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>>>
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>>> PRO testStrutRef
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>>> Compile_Opt idl2
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>>> a = list(findgen(10), /extract)
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>>> a[4] = {value:3.0}
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>>> help, a[4], /struct
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>>> ;a[4].value = 4.0 ;won't work: % Attempt to store into an expression: >
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>>> ;(a[4]).value = 4.0 ;won't work: % Attempt to store into an expression: Structure reference.
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>>> ;((a)[4]).value = 4.0 ;won't work: % Attempt to store into an expression: Structure reference.
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>>> struct = a[4]
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>>> struct.value = 4.0
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>>> a[4] = struct ;works, but not really straight forward...
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>>> print, a
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>>> END
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>>>
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>>> It seems like I can't address a structure element of a list directly.
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>>> Did I misplace my parenthesis? Is there a less cumbersome workaround?
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>>
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>> Seems like a flat-out bug to me. List elements should be "lvalues," as they say in the compile business.
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>> Craig
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>>
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>
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> Yes, seems like a bug. Note that index notation works:
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>
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> IDL> print, (a[4]).(0)
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> 3.00000
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>
>
> Mike
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> --
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> Michael Galloy
>
> www.michaelgalloy.com
>
> Modern IDL: A Guide to IDL Programming (http://modernidl.idldev.com)
>
> Research Mathematician
>
> Tech-X Corporation
The index notation works only for printing, but not for assigning. But printing works also for
print, a[4].value
By the way:
IDL> !version
{
ARCH: "x86_64",
OS: "Win32",
OS_FAMILY: "Windows",
OS_NAME: "Microsoft Windows",
RELEASE: "8.3",
BUILD_DATE: "Nov 15 2013",
MEMORY_BITS: 64,
FILE_OFFSET_BITS: 64
}
Cheers,
Helder
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