[R] Avoiding loops
Charles C. Berry
cberry at tajo.ucsd.edu
Wed Sep 2 17:51:40 CEST 2009
On Tue, 1 Sep 2009, dolar wrote:
>
> Would like some tips on how to avoid loops as I know they are slow in R
>
If I understand your criterion (and calling your data.frame 'dat'):
> criterion <- as.matrix(dist(dat$a)) <= 5 & outer(dat$a,dat$a,">=")
> criterion %*% as.matrix(dat[, c("b","c")])
b c
1 5 2
2 11 11
3 13 14
4 11 14
HTH,
Chuck
> i've got a data frame :
>
> a b c
> 1 5 2
> 4 6 9
> 5 2 3
> 8 3 2
>
> What i'd like is to sum for each value of a, the sum of b and the sum of c
> where a equal to or less than (with a distance of 5)
>
> i.e. for row three
> we have a=5
> i'd like to sum up b and sum up c with the above rule
> since 5, 4 and 1 are less than (within a distance of 5) or equal to 5, then
> we should get the following result:
>
> a b c
> 5 13 14
>
> the overall result should be
> a b c
> 1 5 2
> 4 11 11
> 5 13 14
> 8 11 14
>
> how can i do this without a loop?
> --
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>
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Charles C. Berry (858) 534-2098
Dept of Family/Preventive Medicine
E mailto:cberry at tajo.ucsd.edu UC San Diego
http://famprevmed.ucsd.edu/faculty/cberry/ La Jolla, San Diego 92093-0901
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