On 5/12/2008 2:58 PM, Gabriel Valiente wrote:
Is there any built-in way to lexicographically compare two vectors of
the same length in R? The textbook algorithm could be coded as follows:
lex.cmp <- function (vec1,vec2) {
for (j in 1:length(vec1)) {
if (vec1[j] < vec2[j]) { return(-1) }
if (vec1[j] > vec2[j]) { return(1) }
}
return(0)
}
I don't think there's any standard function for this. You could write
one as above, or slightly faster as
lex.cmp <- function(vec1, vec2) {
index <- which.min(vec1 == vec2) # find the first diff
sign(vec1[index] - vec2[index]) # assumes numeric
}
If you don't want to assume numeric data, you may need to expand that
last line to a series of comparisons like yours, but with index in place
of j, e.g.
if (vec1[index] < vec2[index]) { return(-1) }
if (vec1[index] > vec2[index]) { return(1) }
return(0)
(unless there's a compare function in some package or other.)
Duncan Murdoch
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