| Calculating difference between each element in array from previous [message #83680] |
Fri, 29 March 2013 07:43  |
morganlsilverman
Messages: 46
Registered: February 2013
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Member |
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Hello,
I'm trying to rewrite my code to eliminate for loops as much as possible. I believe I have to have one to start because I'm trying to match a list of dates in one array to a list of dates in another.
for k=0,n_elements(mcity)-1 do begin
indexa = where(strmatch(strmid(adatea,0,8),strmid(mdate(k),0,8)) eq 1,num)
It only seems to work if I go one mdate at a time. Thats fine but I'd like to eliminate the other if statements and for loops within this one to speed up calculations if possible. Once I match the date I need to find out if the array matches a selection of criteria to decide whether to use that array or not.
if num gt 0 then begin ; If matches then go through profile critera
inda = where(finite(aalta(col,row,*)), count) ; Count number of non-NaN altitudes
if (n_elements(inda) ge 15 ) then begin
dcount=0
diffa = fltarr(50)
for k=0,count-2 do begin
diffa(k) = aalta(col,row,inda(k+1))-aalta(col,row,inda(k))
dcount = dcount+1
endfor
diffa = diffa(0:dcount-1)
; Only interested in profiles with altitude differences less than 500 m
if (max(abs(diffa)) lt 500.0) then begin
if (j eq 0) or (j gt 0 and i ne iprev) then begin
jcount = 0
icount = icount + 1
endif else begin
if (j gt 0 and i eq iprev) then begin
jcount = jcount + 1
icount = icount
endif
endelse
; Now do calculations...
endif
endif
endif
endfor
Is there a way to eliminate the diffa loop... and calculate the differences between each altitude another way?
for k=0,count-2 do begin
diffa(k) = aalta(col,row,inda(k+1))-aalta(col,row,inda(k))
dcount = dcount+1
endfor
I've been reading online about eliminating for loops and rebin/reform but haven't been able to figure out what would work best if anything. Thanks.
Sincerely,
Morgan
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| Re: Calculating difference between each element in array from previous [message #83805 is a reply to message #83680] |
Fri, 29 March 2013 19:03  |
dg86
Messages: 118
Registered: September 2012
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Senior Member |
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On Friday, March 29, 2013 8:07:08 PM UTC-4, Phillip Bitzer wrote:
> For a start, I think I see where you are differencing adjacent elements of an array. This can be done without looping:
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> diff = arr - SHIFT(arr, 1)
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> Note SHIFT will wrap around values, so if that's not important you'll want to "mask" this values somehow.
How about
diff = arr - arr[1:*]
This addresses the wrap-around issue.
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