| indexing a structure in a list [message #87472] |
Wed, 05 February 2014 08:36  |
Helder Marchetto
Messages: 520
Registered: November 2011
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Senior Member |
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Hi,
I've got the feeling this should work, but for some reason it isn't.
So here is some code to test the problem with the errors describe in it:
PRO testStrutRef
Compile_Opt idl2
a = list(findgen(10), /extract)
a[4] = {value:3.0}
help, a[4], /struct
;a[4].value = 4.0 ;won't work: % Attempt to store into an expression: Structure reference.
;(a[4]).value = 4.0 ;won't work: % Attempt to store into an expression: Structure reference.
;((a)[4]).value = 4.0 ;won't work: % Attempt to store into an expression: Structure reference.
struct = a[4]
struct.value = 4.0
a[4] = struct ;works, but not really straight forward...
print, a
END
It seems like I can't address a structure element of a list directly.
Did I misplace my parenthesis? Is there a less cumbersome workaround?
Thanks,
Helder
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| Re: indexing a structure in a list [message #87473 is a reply to message #87472] |
Wed, 05 February 2014 09:00  |
David Fanning
Messages: 11724
Registered: August 2001
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Senior Member |
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Helder writes:
> I've got the feeling this should work, but for some reason it isn't.
> So here is some code to test the problem with the errors describe in it:
>
> PRO testStrutRef
> Compile_Opt idl2
> a = list(findgen(10), /extract)
> a[4] = {value:3.0}
> help, a[4], /struct
> ;a[4].value = 4.0 ;won't work: % Attempt to store into an expression: Structure reference.
> ;(a[4]).value = 4.0 ;won't work: % Attempt to store into an expression: Structure reference.
> ;((a)[4]).value = 4.0 ;won't work: % Attempt to store into an expression: Structure reference.
> struct = a[4]
> struct.value = 4.0
> a[4] = struct ;works, but not really straight forward...
> print, a
> END
>
> It seems like I can't address a structure element of a list directly.
> Did I misplace my parenthesis? Is there a less cumbersome workaround?
Yeah, don't know. I'm no expert, but I'm not surprised lists and
structures don't play well together. Have you thought about a hash
instead?
IDL> a = list(findgen(10), /extract)
IDL> a[4] = hash('value', 3.0)
IDL> (a[4])['value'] = 4.0
IDL> print, a[4]
value: 4.00000
Cheers,
David
--
David Fanning, Ph.D.
Fanning Software Consulting, Inc.
Coyote's Guide to IDL Programming: http://www.idlcoyote.com/
Sepore ma de ni thue. ("Perhaps thou speakest truth.")
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| Re: indexing a structure in a list [message #87474 is a reply to message #87472] |
Wed, 05 February 2014 09:52 |
Craig Markwardt
Messages: 1869
Registered: November 1996
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Senior Member |
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On Wednesday, February 5, 2014 11:36:09 AM UTC-5, Helder wrote:
> Hi,
>
> I've got the feeling this should work, but for some reason it isn't.
>
> So here is some code to test the problem with the errors describe in it:
>
>
>
> PRO testStrutRef
> Compile_Opt idl2
> a = list(findgen(10), /extract)
> a[4] = {value:3.0}
> help, a[4], /struct
> ;a[4].value = 4.0 ;won't work: % Attempt to store into an expression: >
> ;(a[4]).value = 4.0 ;won't work: % Attempt to store into an expression: Structure reference.
> ;((a)[4]).value = 4.0 ;won't work: % Attempt to store into an expression: Structure reference.
> struct = a[4]
> struct.value = 4.0
> a[4] = struct ;works, but not really straight forward...
> print, a
> END
>
> It seems like I can't address a structure element of a list directly.
> Did I misplace my parenthesis? Is there a less cumbersome workaround?
Seems like a flat-out bug to me. List elements should be "lvalues," as they say in the compile business.
Craig
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| Re: indexing a structure in a list [message #87475 is a reply to message #87474] |
Wed, 05 February 2014 10:05 |
Michael Galloy
Messages: 1114
Registered: April 2006
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Senior Member |
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On 2/5/14, 10:52 AM, Craig Markwardt wrote:
> On Wednesday, February 5, 2014 11:36:09 AM UTC-5, Helder wrote:
>> Hi,
>>
>> I've got the feeling this should work, but for some reason it isn't.
>>
>> So here is some code to test the problem with the errors describe in it:
>>
>>
>>
>> PRO testStrutRef
>> Compile_Opt idl2
>> a = list(findgen(10), /extract)
>> a[4] = {value:3.0}
>> help, a[4], /struct
>> ;a[4].value = 4.0 ;won't work: % Attempt to store into an expression: >
>> ;(a[4]).value = 4.0 ;won't work: % Attempt to store into an expression: Structure reference.
>> ;((a)[4]).value = 4.0 ;won't work: % Attempt to store into an expression: Structure reference.
>> struct = a[4]
>> struct.value = 4.0
>> a[4] = struct ;works, but not really straight forward...
>> print, a
>> END
>>
>> It seems like I can't address a structure element of a list directly.
>> Did I misplace my parenthesis? Is there a less cumbersome workaround?
>
> Seems like a flat-out bug to me. List elements should be "lvalues," as they say in the compile business.
> Craig
>
Yes, seems like a bug. Note that index notation works:
IDL> print, (a[4]).(0)
3.00000
Mike
--
Michael Galloy
www.michaelgalloy.com
Modern IDL: A Guide to IDL Programming (http://modernidl.idldev.com)
Research Mathematician
Tech-X Corporation
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| 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,
>
>>>
>
>>> I've got the feeling this should work, but for some reason it isn't.
>
>>>
>
>>> So here is some code to test the problem with the errors describe in it:
>
>>>
>
>>>
>
>>>
>
>>> PRO testStrutRef
>
>>> Compile_Opt idl2
>
>>> a = list(findgen(10), /extract)
>
>>> a[4] = {value:3.0}
>
>>> help, a[4], /struct
>
>>> ;a[4].value = 4.0 ;won't work: % Attempt to store into an expression: >
>
>>> ;(a[4]).value = 4.0 ;won't work: % Attempt to store into an expression: Structure reference.
>
>>> ;((a)[4]).value = 4.0 ;won't work: % Attempt to store into an expression: Structure reference.
>
>>> struct = a[4]
>
>>> struct.value = 4.0
>
>>> a[4] = struct ;works, but not really straight forward...
>
>>> print, a
>
>>> END
>
>>>
>
>>> It seems like I can't address a structure element of a list directly.
>
>>> Did I misplace my parenthesis? Is there a less cumbersome workaround?
>
>>
>
>> Seems like a flat-out bug to me. List elements should be "lvalues," as they say in the compile business.
>
>> Craig
>
>>
>
>
>
> Yes, seems like a bug. Note that index notation works:
>
>
>
> IDL> print, (a[4]).(0)
>
> 3.00000
>
>
>
> Mike
>
> --
>
> 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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