Split vector of strings and paste subset of resulting elements into a new vector

Question

Define

z<- as.character(c(\"1_xx xx xxx_xxxx_12_sep.xls\",\"2_xx xx xxx_xxxx_15_aug.xls\"))

such that

> z
[1] \"1_xx xx x         


        

Answer 1

One call to gsub (and some regex magic based on @Andrie's answer) can do this. See ?regexp for details on what I used in the pattern and replacement (back-reference) arguments.

gsub("^(\\d+_).*_(\\d+_\\w*).xls", "\\1\\2", z)
# [1] "1_12_sep" "2_15_aug"