R split string at last whitespace chars using tidyr::separate

Question

Suppose I have a dataframe like this:

df<-data.frame(a=c(\"AA\",\"BB\"),b=c(\"short string\",\"this is the longer string\"))

I would like to

Answer 1

You may turn the [^ ]*$ part of your regex into a (?=[^ ]*$) non-consuming pattern, a positive lookahead (that will not consume the non-whitespace chars at the end of the string, i.e. they won't be put into the match value and thus will stay there in the output):

df%>%
  separate(b,c("partA","partB"),sep=" (?=[^ ]*$)")

Or, a bit more universal since it matches any whitespace chars:

df %>%
  separate(b,c("partA","partB"),sep="\\s+(?=\\S*$)")

See the regex demo and its graph below:

Output:

   a              partA  partB
1 AA              short string
2 BB this is the longer string