| Re: What are the rules for automatic removal of singleton dimensions, and can I have a way of disabling them, please? [message #82791 is a reply to message #82553] |
Thu, 17 January 2013 00:11   |
tom.grydeland
Messages: 51
Registered: September 2012
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On Wednesday, January 16, 2013 12:09:45 PM UTC+1, Tom Grydeland wrote:
Since I'm talking to myself here, I might as well reply to myself also.
> (Of course, in line with Mats Löfdahl's suggestion earlier, TRANSPOSE could also be modified to add back singleton dimensions to its input array as necessary.)
Having written this, I decided to go ahead and do it that way also, just to see. It feels a little bit like I'm fixing IDL's bugs for them instead of working on the problems I'm actually paid to solve. I tried writing MY_TRANSPOSE so that it can be a drop-in replacement of TRANSPOSE, i.e. it shall give exactly the same results as TRANSPOSE for every input that TRANSPOSE will accept.
The tedium of adding singleton dimensions was factored out to a function ATLEAST_N_DIM, which modifies and returns its first argument.
I'm putting these functions out there for anyone to see or use as they see fit.
I am still hopeful that I can get a COMPILE_OPT that would (within a certain scope) disable stripping of trailing singleton dimensions, so I wouldn't have to resort to such hackery or the replacement of base IDL functionality.
Stylistic comments, suggestions, etc?
;+
; Small utility that ensures its input array has dimensionality at least N.
; Modifies _and_ returns its input, without making copies.
;
; :Params:
; a: in, out
; array to modify dimensionality of
; n: in, type=integer
; minimum number of dimensions for result
;
; :Returns:
; a, with zero or more singleton dimensions appended
;
; :See also:
; MY_TRANSPOSE, DENSEGRID
;-
function atleast_n_dim, a, n
adim = size(a, /dimensions)
if n_elements(adim) ge n then return, a
adim = [adim, make_array(n-n_elements(adim), value=1)]
a = reform(a, adim, /overwrite)
return, a
end
;+
; Version of TRANSPOSE that will add singleton dimensions if needed
;
; :See also:
; ATLEAST_N_DIM, DENSEGRID
;-
function my_transpose, arr, perm
;; defer simple cases to native TRANSPOSE
if n_elements(perm) eq 0 then return, transpose(arr)
adims = size(arr, /dimensions)
np = max(perm)+1
na = n_elements(adims)
if np le na then return, transpose(arr, perm)
narr = transpose(atleast_n_dim(arr, np), perm)
;; set dimensions of arr back to what they were
arr = reform(arr, adims, /overwrite)
return, narr
end
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