pro filtzero,a,b,n

;Created 4/9/98 by C See
;This program filters out the common zero elements of arrays a & b
;and returns the resulting array size as n.
;a and b must be the unidimensional and have the same size.
;if all elements are zero, the programs returns n=0 and the arrays,
; a & b are untouched.

sa=size(a)
sb=size(b)

dima=sa(sa(0))
dimb=sb(sb(0))

if dima ne dimb then begin
 print,'filtzero called with disparent arrays'
 goto, exit
endif

;pack all the data into the top of the arrays...
i=0	;i steps through array's
n=dima	;n holds the size of the final array

again:
while i lt n do begin
 if a(i) eq 0. and b(i) eq 0. then begin
  if dima eq 1 then goto,shorten_array		;one element, zero array set
  if i eq dima-1 then begin			;last set are 0,0
   n=n-1
   goto,shorten_array
  endif
  a(i:dima-1)=[a(i+1:dima-1),0] & b(i:dima-1)=[b(i+1:dima-1),0]	;moves data up one set
  n=n-1
  goto,again
 endif
 i=i+1
endwhile

shorten_array:
;shorten_array to the size of the valid data...
if n eq 0 then goto,exit	;if all elements are zero
a1=fltarr(n)
b1=fltarr(n)
a1=a(0:n-1)
b1=b(0:n-1)
a=fltarr(n)
b=fltarr(n)
a=a1 & b=b1


exit:
return
end