[R] millions of comparisons, speed wanted

[Adrian DUSA]

Dear Andy,

On Thursday 15 December 2005 20:57, Liaw, Andy wrote:
> Just some untested idea:
> If the data are all 0/1, you could use dist(input, method="manhattan"), and
> then check which entry equals 1.  This should be much faster than creating
> all pairs of rows and check position-by-position.

Thanks for the idea, I played a little with it. At the beginning yes, the data 
are all 0/1, but during the minimizing iterations there are also "x" values; 
for example comparing:
0 1 0 1 1
0 0 0 1 1
should return
0 "x" 0 1 1

whereas
0 "x" 0 1 1
0 0 0 1 1
shouldn't even be compared (they have different number of figures).

Replacing "x" with NA in dist is not yielding results either, as with
NA 0 0 1 1
0 0 0 1 1
dist returns 0.

I even wanted to see if I could tweak the dist code, but it calls a C program 
and I gave up.

Nice idea anyhow, maybe I'll find a way to use it further.
Best,
Adrian

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Adrian DUSA
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