| Re: Still missing features in IDL 8 [message #73216 is a reply to message #72871] |
Sun, 31 October 2010 17:00  |
penteado
Messages: 866
Registered: February 2018
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Senior Member
Administrator |
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On Oct 13, 2:38 pm, Chris Torrence <gorth...@gmail.com> wrote:
> Regarding #2, what if you could use additional indices to access array
> elements within lists?
>
> For example:
>
> IDL> a = LIST(FINDGEN(10), BYTARR(5,3))
> IDL> help, a[0]
> <Expression> FLOAT = Array[10]
> IDL> help, a[0,3] ; currently throws an error in IDL8.0
> <Expression> FLOAT = 3.00000
> IDL> a[0,3] = !pi ; currently throws an error in IDL8.0
>
> IDL> help, a[1]
> <Expression> BYTE = Array[5, 3]
> IDL> help, a[1,4,2] ; currently throws an error in IDL8.0
> <Expression> BYTE = 0
> IDL> a[1,4,2] = 255 ; currently throws an error in IDL8.0
>
> So the first index would give the list element, and the remaining
> indices would index into the array itself. Obviously you could only
> have up to 7 dimensions in your contained array, but that probably
> isn't a huge limitation.
I was writing a class like that, inheriting from list, and that
brought me a question: Should the extra dimension (of the list index)
be on the left, as above, or on the right?
The notation (already valid for retrieving values) (a[1])[0] suggests
that the array index should come on the left. However, writing a[1,0]
suggests array dimensions, in which case the list index would make
more sense on the right, as the list dimension is the slowest-varying
one.
Tough it would be a bit incoherent with the array dimension order, it
seems to me that it is better to have the list index on the left. That
way,
print,(a[1])[0] ;already valid
would be the same as
print,a[1,0]
instead of the more confusing
print,a[0,1]
Any thoughts on that?
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