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Re: Undocumented array indexing feature? [message #14105 is a reply to message #14104]

Fri, 22 January 1999 00:00

J.D. Smith
Messages: 214
Registered: August 1996

Senior Member

Liam Gumley wrote:
>
> Liam Gumley wrote:
>> Here's a way to index an array I hadn't seen before:
>>
>> a = indgen(10,10)
>> x = [3,5,8,9]
>> y = [2,7]
>> print, (a[x,*])[*,y]
>> 23 25 28 29
>> 73 75 78 79
>>
>> Does anyone know where this feature (i.e. enclosing an array with
>> parentheses and appending an index) is documented? I couldn't find it in
>> my printed IDL 5.0 documentation.
>
> To answer my own question, a careful reading of Chapter 5 of 'Building
> IDL Applications' p. 60
> (ftp://ftp.rsinc.com/pub/idl_5.2/info/docs/building.pdf)
> revealed the following:
>
> "The syntax of a subscript reference is:
> Variable_Name[Subscript_ List]
> or
> (Array_Expression)[Subscript_List]"
>
> Thanks to Bill and Craig for their replies.
>

Array indexing isn't the only place parentheses are useful...

try this sometime:

a=(b=(c=1))

Basically, parentheses just instruct the command parser to iterate as
many times as necessary to remove them all. Other examples:

print,(x=5)

It doesn't work for everything though... as evidenced by:

z=5+6*(y=8)

JD

--
J.D. Smith |*| WORK: (607) 255-5842
Cornell University Dept. of Astronomy |*| (607) 255-6263
304 Space Sciences Bldg. |*| FAX: (607) 255-5875
Ithaca, NY 14853 |*|

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[Message index]

		Re: Undocumented array indexing feature? By: wbiagiot on Mon, 25 January 1999 00:00
		Re: Undocumented array indexing feature? By: Alex Schuster on Mon, 25 January 1999 00:00
		Re: Undocumented array indexing feature? By: Mark Buckley on Mon, 25 January 1999 00:00
		Re: Undocumented array indexing feature? By: wrb1000 on Mon, 25 January 1999 00:00
		Re: Undocumented array indexing feature? By: Mark Buckley on Mon, 25 January 1999 00:00
		Re: Undocumented array indexing feature? By: Robert S. Hill on Fri, 22 January 1999 00:00
		Re: Undocumented array indexing feature? By: J.D. Smith on Fri, 22 January 1999 00:00
		Re: Undocumented array indexing feature? By: Liam Gumley on Fri, 22 January 1999 00:00
		Re: Undocumented array indexing feature? By: wbiagiot on Thu, 21 January 1999 00:00
		Re: Undocumented array indexing feature? By: Craig Markwardt on Thu, 21 January 1999 00:00

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