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Unexpected array subscript truncation [message #68881]

Mon, 30 November 2009 13:03

M. Katz
Messages: 69
Registered: May 2005

Member

Here's an interesting little array trick I discovered by accident. It
doesn't give an error message where I would expect one! Try this:

* As a warm-up enter this and see that IDL does complain.

a = intarr(3,3)
a[0,5] = 1

* Now try to set it as follows, with an array of y-index values.

a[0,[0,5]] = 1
print, a
1 0 0
0 0 0
1 0 0

No complaint! In fact, IDL quietly truncated the 5 down to its highest
allowed value, which is 2.

It also works like this:

a[*,[0,9]] = 3

is equivalent to

a[*,[0,2]] = 3

The same truncation happens with x indices as well.

I suppose there could be some cases where this would not be the
desired behavior. Any thoughts? Am I missing something?

-M.

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