[R] Re gular Expression help
Waclaw.Marcin.Kusnierczyk at idi.ntnu.no
Sat Nov 8 22:28:54 CET 2008
Wacek Kusnierczyk wrote:
> Gabor Grothendieck wrote:
>> Here are a few more solutions. x is the input vector
>> of character strings.
>> The first is a slightly shorter version of one of Wacek's.
>> The next three all create an anonymous grouping variable
>> (using sub, substr/gsub and strapply respectively)
>> whose components are "p" and "q" and then tapply
>> is used to separate out the corresponding components
>> of x according to the grouping:
>> sapply(c(p = "^[^pq]*p", q = "^[^pq]*q"), grep, x = x, value = TRUE)
>> tapply(x, sub("^[^pq]*(.).*", "\\1", x), c)
>> tapply(x, substr(gsub("[^pq]", "", x), 1, 1), c)
>> tapply(x, strapply(x, "^[^pq]*(.)", simplify = c), c)
> wow! cool stuff. if you're interested in comparing their efficiency,
> source the attached script.
using lapply with side-effects code should probably be considered bad
practice, so replace lapply with a for loop. sorry.
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