This is a multi-part message in MIME format.
--------------66221E172010
Content-Type: text/plain; charset=us-ascii
Content-Transfer-Encoding: 7bit
David Fanning wrote:
>>> Given vectors of the type...
>>>
>>> a = [1,2,3,4,5]
>>> b = [3,4,5,6,7]
>>>
>>> What is the most efficient way to determine which values that occur in
>>> a also occur in b (i.e., the values [3,4,5] occur in both a and b).
> I don't know if this is the most efficient way (it probably isn't),
> but this is my off-the-cuff way of solving this problem.
>
> FUNCTION A_in_B, a, b
> num = N_Elements(a)
> vector = FltArr(num)
> FOR j=0,num-1 DO BEGIN
> index = Where(a(j) EQ b, count)
> IF count GT 0 THEN vector(j) = 1 ELSE vector(j)=0
> ENDFOR
> solution = a(Where(vector EQ 1))
> RETURN, solution
> END
>
> When I run the example case above, I get a vector with the values
> [3,4,5].
Here's a routine, called SYNCHRONIZE, that I whipped up thanks to some
help from RSI. I had the problem of two data streams, each with a
structure with a tag called "dwell" that needed matching up. This
routine works great except possibly for some funny behavior if a given
number is repeated in a data stream (nah, that shouldn't happen in real
data). If you don't need the full-blown procedure, the guts of the
algorithm should be obvious.
--
Dr. Marty Ryba | Of course nothing I say here is official
MIT Lincoln Laboratory | policy, and Laboratory affililaton is
ryba@ll.mit.edu | for identification purposes only,
| blah, blah, blah, ...
--------------66221E172010
Content-Type: text/plain; charset=us-ascii; name="synchronize.pro"
Content-Transfer-Encoding: 7bit
Content-Disposition: inline; filename="synchronize.pro"
;+
; Name:
; SYNCHRONIZE
; Purpose:
; Match up two arrays of structures by a tag name
; Usage:
; synchonize,a,b[,ause=ause][,buse=buse][,keywords=values]
; Inputs:
; A & B are arrays of structures to be sychronized. They are
; returned containing only those members that match within the
; specified tolerance for the tag fields being matched.
; Optional Keyword Inputs:
; tags - String array containing the tag names to match by. Defaults
; to ['dwell','dwell']. Case insensitive.
; tolerance - Maximum difference to declare a match. All comparisions
; are double precision. Defaults to 0.0 (exact match).
; Optional Outputs:
; ause - Set of array indicies used to convert input A to output A.
; Useful if you have 2 already synchonized arrays and need to
; synch a third.
; buse - Same for B
; Restrictions:
; The structures should have only one member with the tag name given.
; If there are multiple structure members with the same tag, SYNCHRONIZE
; will use the first.
; Cannot use tags from nested structures.
; Modification History:
; M.F. Ryba, MIT/LL, June 93, Created from algorithm written by David
; Stern of RSI.
; M.F. Ryba, Jan 95, added TEMPORARY and check for whether the
; structure is shortened.
;-
PRO Synchronize, a, b, ause=ause, buse=buse, tags=tags, tolerance=tolerance, $
help=help
IF keyword_set(help) THEN BEGIN
doc_library, 'synchronize'
return
ENDIF
IF n_elements(tags) EQ 0 THEN tags = ['dwell', 'dwell']
IF n_elements(tolerance) EQ 0 THEN tolerance = 0.0d
tags = strupcase(tags)
atags = tag_names(a)
btags = tag_names(b)
ai = where(atags EQ tags(0), cnt)
IF cnt EQ 0 THEN BEGIN
string = 'Tag '+tags(0)+' not found in structure A'
message, string
ENDIF
IF cnt GT 1 THEN BEGIN
string = 'Structure A has more than 1 tag named '+tags(0)+ $
'; will use the first'
message, string, /informational
ENDIF
bi = where(btags EQ tags(1), cnt)
IF cnt EQ 0 THEN BEGIN
string = 'Tag '+tags(1)+' not found in structure B'
message, string
ENDIF
IF cnt GT 1 THEN BEGIN
string = 'Structure B has more than 1 tag named '+tags(1)+ $
'; will use the first'
message, string, /informational
ENDIF
ai = ai(0) & bi = bi(0)
tmp = [double(a.(ai)), double(b.(bi))]
sortab = sort(tmp)
tmp = tmp(sortab)
match = where((tmp(1:*) - tmp) LE tolerance, cnt)
IF cnt GT 0 THEN BEGIN
aeq = sortab(match)
beq = sortab(match+1)
tmp = aeq < beq
beq = (beq > aeq) - n_elements(a)
aeq = tmp
IF n_elements(aeq) NE n_elements(a) THEN a = (temporary(a))(aeq)
IF n_elements(beq) NE n_elements(b) THEN b = (temporary(b))(beq)
ause = aeq
buse = beq
ENDIF ELSE BEGIN
print, 'No matches found between A.'+tags(0)+' and B.'+tags(1)
ause = -1
buse = -1
ENDELSE
return
END
--------------66221E172010--
|
comp.lang.idl-pvwave archive
Members
Search
Help
Login
Home
