| Re: Do you find this weird too? [message #56851 is a reply to message #56850] |
Mon, 19 November 2007 02:45   |
lasse
Messages: 48
Registered: February 2007
|
Member |
|
|
On 19 Nov, 10:36, Allan Whiteford
<allan.rem...@phys.remove.strath.ac.remove.uk> wrote:
> Lasse,
>
> From "Using arrays as subscripts":
>
> "Clipping
> If an element of the subscript array is less than or equal to zero, the
> first element of the subscripted array is selected. If an element of the
> subscript array is greater than or equal to the last subscript in the
> subscripted array, the last element is selected. "
>
> this is what it's supposed to do although I've never found any kind of
> use for it.
>
> You can say scary things like:
>
> a=findgen(50)
> a[[100]]=7 ; not the same as a[100]=7
> print,a[49]
>
> for me, it throws away all the nice error checking you thought you had
> for arrays overrunning.
>
> Thanks,
>
> Allan
>
> Lasse Clausen wrote:
>> Hi there,
>
>> hope this gets through to you guys, now with all the spam and whatnot.
>> Anywho, maybe this has come up before, here is some code
>
>> aa = randomu(12L, 200, 100)
>> ff = findgen(100)
>> maxs = max(aa, maxind, dimension=2)
>> print, maxind[0:10]
>> help, ff[maxind[0:10]]
>> plot, ff[maxind[0:10]]
>
>> Now I find this weird, because maxind is an array of longs clearly
>> bigger than the size of ff but IDL does not complain and plots
>> something (btw not what I want but this is solved with array_indices).
>> Is this something to do with the fact that maxind is a 1D
>> representation of 2D array indices? I hope it is because otherwise why
>> does IDL not fall over complaining that maxind[0], which on my machine
>> is 19200, is bigger than the size of ff.
>
>> Mhmm
>
>> print, ff[maxind[0]]
>
>> falls over
>
>> print, ff[maxind[0:1]]
>
>> doesn't.
>
>> btw print, !version
>> { x86 linux unix linux 6.2 Jun 20 2005 32 64}
>
>> Cheers
>> Lasse
What the...?! Well, I guess somebody thought this was a good idea.
Makes no sense to me since you could achieve the same behaviour using
the < or > operator. Subscripting an array with an index smaller than
zero or bigger than the size of the array is just wrong and should
produce an error.
But thanks, I will keep this useful fact in mind.
Cheers
Lasse
|
|
|
|
comp.lang.idl-pvwave archive
Members
Search
Help
Login
Home
