| Distance between two sets of datapoints [message #70257] |
Thu, 25 March 2010 03:33 |
Maxwell Peck
Messages: 61
Registered: February 2010
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Hi All,
I have two sets of data points, inputa and inputb, inputa has many
more data points than the other. I need to find the distance between
each point in inputa and all the points in inputb (hopefully without
loops). At the moment I am using parts of distance_measure.pro to
generate the full set of distances and subsetting indexes as required.
The code follows. I can't see an easy way of generating the indexes
though so that only the pairs i want are calculated (i.e. not
calculating between inputb/inputb or inputa/inputa indexes).
inputa and inputb can be very very large so I don't think i can use a
matrix approach to do it vectorially and looping seems awfully slow.
An alternative approach or other suggestions would be appreciated.
Regards
Max
inputa = findgen(2,10)
inputb = findgen(2,2)
t = [[inputa],[inputb]]
m=n_elements(t)/2
n = m*(m-1)/2
ii = 0L
index0 = LINDGEN(m - 1) + 1 ; work array
index1 = LONARR(n, /NOZERO)
index2 = LONARR(n, /NOZERO)
for i=0,m-2 do begin
n1 = m - (i+1)
index1[ii:ii+n1-1] = i
index2[ii] = index0[0:n1-1] + i
ii += n1
endfor
diff = abs(t[*,index1] - t[*,index2])
res = sqrt(TOTAL(diff^2, 1))
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