[ncl-talk] An "2d" Attribute Array Conundrum

[Alan Brammer]

To piggyback on Phillipe's email. I just coincidentally came across this
problem myself, worse though I get seg faults.

Easy work around but seg faults are never good.

e.g.

res = True
res at test := new( (/10,10/) , float)
; print(res at test(0,3)) ;;; we can't do this, so is it actually a 1d array?
print(res at test(3))  ;; Seg fault.


~alan



On 13 May 2015 at 17:01, Philippe Papin <ppapin at albany.edu> wrote:

> Hi David,
>
> Thanks for the detailed reply and suggestions. I can easily assign the
> attribute values to a local variable! Also good to know that 2d arrays are
> allowed in attributes even if the are not fully supported!
>
> Have a great day!
> -Philippe
>
> On Wed, May 13, 2015 at 2:17 PM, David Brown <dbrown at ucar.edu> wrote:
>
>> Hi Phillipe,
>> That's a good question. Actually the error message, as you discovered,
>> is a bit misleading. NCL was originally designed to only allow 1D
>> attributes in keeping with the NetCDF data model. Later, however, when
>> we needed the ability to transmit 2D coordinate information to the
>> graphics routines (mainly), we loosened the restriction to allow NCL
>> variables to have multi-d attributes as a convenience. However, as you
>> have found, we did not implement full support for this feature. Partly
>> this is because you cannot write such an attribute to any of the
>> output file formats we support -- so it can never be truly integrated
>> into the data model.
>> Practically speaking, if you wanted to have a routine that handles
>> subscripting of 2D attributes, I'm guessing you could do it by
>> assigning the attribute value to a local variable, subscripting the
>> variable, and using the 'reassign' syntax to give the attribute its
>> new subscripted value.
>> We will try to make the error message a little more informative.
>> Eventually maybe we can make subscripting work in this situation.
>>  -dave
>>
>> On Wed, May 13, 2015 at 10:56 AM, Philippe Papin <ppapin at albany.edu>
>> wrote:
>> > Hi NCL-talk,
>> >
>> > I came across a strange conundrum today when testing some code. I use
>> > attributes in my code to send 1d variables through attributes into
>> > subroutines without explicitly defining it in the new subroutine. This
>> > practice is limited to 1d arrays since attributes in theory can only be
>> 1d.
>> > However, if this is the case, why can you "create" a 2d attribute array
>> and
>> > then print this attribute array without error?
>> >
>> > Here is a code snippet of an example of what I am talking about. I'm
>> using
>> > NCL version 6.2.1
>> >
>> > opt = True
>> > array2d = (/ (/1,2,3/) , (/4,5,6/) /)
>> > opt at array2d = array2d
>> > print(opt at array2d) ;;; output below seem to print out array correctly
>> in 2d
>> >
>> > (0,0) 1
>> >
>> > (0,1) 2
>> >
>> > (0,2) 3
>> >
>> > (1,0) 4
>> >
>> > (1,1) 5
>> >
>> > (1,2) 6
>> >
>> > However if you try to actually subscript the data, you get an error
>> message
>> > that attributes only have one dimension.
>> >
>> > subarray2d = opt at array2d(0,1)
>> >
>> > fatal:Attributes only have one dimension, 2 subscripts used
>> >
>> > fatal:["Execute.c":8576]:Execute: Error occurred at or near line 6
>> >
>> > This is a bit counterintuitive to me. Perhaps the 2d attribute array I
>> > created is really 1d, but just gives the appearance of a 2d array when
>> > printed. Sorry if this is a trivial question, but hopefully that means
>> it
>> > won't take much to figure out what is going on here.
>> >
>> > Thanks for any additional information!
>> >
>> > -Philippe
>> >
>> >
>> > --
>> > -------------------------------------
>> > Philippe P. Papin
>> > Dept. of Atmospheric and Environmental Sciences
>> > University at Albany, SUNY
>> > 1400 Washington Ave, Albany, NY 12222
>> > http://www.atmos.albany.edu/student/ppapin/
>> >
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>
>
>
> --
> -------------------------------------
> Philippe P. Papin
> Dept. of Atmospheric and Environmental Sciences
> University at Albany, SUNY
> 1400 Washington Ave, Albany, NY 12222
> http://www.atmos.albany.edu/student/ppapin/
>
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