R: strsplit on backslash (\)

问题

I am trying to extract the part of the string before the first backslash but I can't seem to get it tot work properly.

I have tried multiple ways of getting it to work, based on the manual page for strsplit and after searching online.

In my actual situation the strings are in a dataframe which I get from a database connection but I can simplify the situation with the following:

> strsplit("BLAAT1\022E:\\BLAAT2\\BLAAT3","\\",fixed=TRUE)
[[1]]
[1] "BLAAT1\022E:" "BLAAT2"      "BLAAT3"  

> strsplit("BLAAT1\022E:\\BLAAT2\\BLAAT3","\\",fixed=FALSE)
Error in strsplit("BLAAT1\022E:\\BLAAT2\\BLAAT3", "\\", fixed = FALSE) : 
  invalid regular expression '\', reason 'Trailing backslash'

> strsplit("BLAAT1\022E:\\BLAAT2\\BLAAT3","\\\\",fixed=TRUE)
[[1]]
[1] "BLAAT1\022E:\\BLAAT2\\BLAAT3"

> strsplit("BLAAT1\022E:\\BLAAT2\\BLAAT3","\\\\",fixed=FALSE)
[[1]]
[1] "BLAAT1\022E:" "BLAAT2"       "BLAAT3"      

The expected output would also split on the \ between BLAAT1 and 022E:

Thanks in advance

回答1:

Here is a regex that you can use: it splits at \ and a non-printable character:

strsplit("BLAAT1\022E:\\BLAAT2\\BLAAT3","[\\\\]|[^[:print:]]",fixed=FALSE)
# [1] "BLAAT1" "E:"     "BLAAT2" "BLAAT3"

See IDEONE demo

来源：https://stackoverflow.com/questions/33210280/r-strsplit-on-backslash