| Skeleton of a new array slicing function [message #15560] |
Thu, 20 May 1999 00:00 |
Martin Schultz
Messages: 515
Registered: August 1997
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Senior Member |
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Liam Gumley wrote:
>
> [...]
I thought this would be something to get started on right away.
Before I rush home
now to celebrate my little daughter's birthday, I'll just "throw" my
version of arrex at you. lease find it attached. It doesn't do anythiong
useful yet, but it should have all of the error checking and setting of
default parameters. Whoever finishes, please let me know, i.e. post it
here.
Thanks,
Martin.
|||||||||||||||\\\\\\\\\\\\\-------------------///////////// //|||||||||||||||
Martin Schultz, DEAS, Harvard University, 29 Oxford St., Pierce 109,
Cambridge, MA 02138 phone (617) 496 8318 fax (617) 495 4551
e-mail mgs@io.harvard.edu web http://www-as/people/staff/mgs/
function arrex,Array,Starti,Endi,Stride,Reform=DoReform
; return quietly if array is undefined or a scalar
if (n_elements(Array) lt 2) then $
return,Array
; get array dimensions
NDims = size( Array, /N_Dimensions )
Dims = size( Array, /Dimensions )
; ### DEBUG
help,Array
; check parameters and set defaults
; if parameter is not present use
; 0 as default for Starti
; Dim[i] as default for Endi
; 1 as default for Stride
; if parameter has less dimensins than Array fill
; remainder with defaults
; if Starti or Endi are negative (-1) use defaults
; A Stride of -1 reverses the respective array dimension
; NOTE that Start indices may be smaller than end indices
; in this case.
DStart = lonarr(NDims) ; array with 0
DEnd = Dims - 1L ; last elements
DStride = lonarr(NDims) + 1L ; every element
if (n_elements(Starti) gt 0) then begin
if (n_elements(Starti) gt NDims) then begin
message,'START contains more numbers than ARRAY dimensions!', $
/Continue
return, Array
endif
; since default is 0 anyway, only copy values in Starti that
; are greater zero
ind = where(Starti gt 0L)
if (ind[0] ge 0) then $
DStart[ind] = ( Starti[ind] < Dims[ind] )
endif
; ### DEBUG
print,'Start indices: ',fix(DStart)
if (n_elements(Endi) gt 0) then begin
if (n_elements(Endi) gt NDims) then begin
message,'END contains more numbers than ARRAY dimensions!', $
/Continue
return, Array
endif
; Only copy values in Endi that are at least zero
ind = where(Endi ge 0L)
if (ind[0] ge 0) then $
DEnd[ind] = ( Endi[ind] < Dims[ind] )
endif
; ### DEBUG
print,'End indices: ',fix(DEnd)
if (n_elements(Stride) gt 0) then begin
if (n_elements(Stride) gt NDims) then begin
message,'STRIDE contains more numbers than ARRAY dimensions!', $
/Continue
return, Array
endif
; Only copy values in Endi that are not zero
ind = where(Stride ne 0L)
if (ind[0] ge 0) then $
DStride[ind] = Stride[ind]
endif else begin ; change default to include negative strides
; where ENDI lt STARTI
ind = where(DEnd lt DStart)
if (ind[0] ge 0) then $
DStride[ind] = -1L
endelse
; ### DEBUG
print,'Stride: ',fix(DStride)
; For extraction, change Stride to all positive, but save
; info which dimensions shall be reversed
NeedReverse = intarr(NDims)
ind = where(DStride lt 0)
if (ind[0] ge 0) then $
NeedReverse[ind] = 1
DStride = abs(DStride)
; ****** actual extraction goes here ******
Result = Array
; Reverse as needed
; ** NOTE: just discovered that IDL's reverse function only handles
; ** up to 3-dimensional arrays !!
if (NDims gt 3) then begin
message,'More than 3 dimensions! Cannot reverse!',/Continue
return,Result
endif
; Apply reform if requested
if (keyword_set(DoReform)) then $
Result = reform(temporary(Result))
return,Result
end
-
Attachment: arrex.pro
(Size: 3.18KB, Downloaded 54 times)
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