Extract numeric part of strings of mixed numbers and characters in R

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The stringr package has lots of handy shortcuts for this kind of work:

# input data following @agstudy
data <-  c('Ab_Cd-001234.txt','Ab_Cd-001234.txt')

# load library
library(stringr)

# prepare regular expression
regexp <- "[[:digit:]]+"

# process string
str_extract(data, regexp)

Which gives the desired result:

  [1] "001234" "001234"

To explain the regexp a little:

[[:digit:]] is any number 0 to 9

+ means the preceding item (in this case, a digit) will be matched one or more times

This page is also very useful for this kind of string processing: http://en.wikibooks.org/wiki/R_Programming/Text_Processing

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