R: removing numbers at begin and end of a string

Question

I\'ve got the following vector:

words <- c(\"5lang\",\"kasverschil2\",\"b2b\")

I want to remove \"5\" in \"5lang\"

Answer 1

 gsub("^\\d+|\\d+$", "", words)    
 #[1] "lang"        "kasverschil" "b2b"

Another option would be to use stringi

 library(stringi)
 stri_replace_all_regex(words, "^\\d+|\\d+$", "")
  #[1] "lang"        "kasverschil" "b2b"        

Using a variant of the data set provided by the OP here are benchmarks for 3 three main solutions (note that these strings are very short and contrived; results may differ on a larger, real data set):

words <- rep(c("5lang","kasverschil2","b2b"), 100000)

library(stringi)
library(microbenchmark)

GSUB <- function() gsub("^\\d+|\\d+$", "", words)
STRINGI <- function() stri_replace_all_regex(words, "^\\d+|\\d+$", "")
GREGEXPR <- function() {
    gregexpr(pattern='(^[0-9]+|[0-9]+$)', text = words) -> mm
    sapply(regmatches(words, mm, invert=TRUE), paste, collapse="") 
}

microbenchmark( 
    GSUB(),
    STRINGI(),
    GREGEXPR(),
    times=100L
)

## Unit: milliseconds
##        expr       min        lq    median        uq       max neval
##      GSUB()  301.0988  349.9952  396.3647  431.6493  632.7568   100
##   STRINGI()  465.9099  513.1570  569.1972  629.4176  738.4414   100
##  GREGEXPR() 5073.1960 5706.8160 6194.1070 6742.1552 7647.8904   100

Answer 2

You can use gsub which uses regular expressions:

gsub("^[0-9]|[0-9]$", "", words)
# [1] "lang"        "kasverschil" "b2b"

Explanation:

The pattern ^[0-9] matches any number at the beginning of a string, while the pattern [0-9]$ matches any number at the end of the string. by separating these two patterns by | you want to match either the first or the second pattern. Then, you replace the matched pattern with an empty string.

Answer 3

Get instances where numbers appear at the beginning or end of a word and match everything else. You need to collapse results because of possible multiple matches:

gregexpr(pattern='(^[0-9]+|[0-9]+$)', text = words) -> mm
sapply(regmatches(words, mm, invert=TRUE), paste, collapse="")