truncate string from a certain character in R [dup

问题:

This question already has answers here:

How do I specify a dynamic position for the start of substring? (4 answers)

Closed 2 years ago.

I have a list of strings in R which looks like:

WDN.TO
WDR.N
WDS.AX
WEC.AX
WEC.N
WED.TO

I want to get all the postfix of the strings starting from the character ".", the result should look like:

.TO
.N
.AX
.AX
.N
.TO

Anyone have any ideas?

回答1:

Joshua's solution works fine. I'd use sub instead of gsub though. gsub is for substituting multiple occurrences of a pattern in a string - sub is for one occurrence. The pattern can be simplified a bit too:

> x <- c("WDN.TO","WDR.N","WDS.AX","WEC.AX","WEC.N","WED.TO")
> sub("^[^.]*", "", x)
[1] ".TO" ".N"  ".AX" ".AX" ".N"  ".TO"

...But if the strings are as regular as in the question, then simply stripping the first 3 characters should be enough:

> x <- c("WDN.TO","WDR.N","WDS.AX","WEC.AX","WEC.N","WED.TO")
> substring(x, 4)
[1] ".TO" ".N"  ".AX" ".AX" ".N"  ".TO"

回答2:

Using gsub:

x <- c("WDN.TO","WDS.N")
# replace everything from the start of the string to the "." with "."
gsub("^.*\\.",".",x)
# [1] ".TO" ".N" 

Using strsplit:

# strsplit returns a list; use sapply to get the 2nd obs of each list element
y <- sapply(strsplit(x,"\\."), `[`, 2)
# since we split on ".", we need to put it back
paste(".",y,sep="")
# [1] ".TO" ".N"

回答3:

Strsplit might do it but in case the data set is too large it will show an error subscript out of bounds

x <- c("WDN.TO","WDR.N","WDS.AX","WEC.AX","WEC.N","WED.TO")
y <- strsplit(x,".")[,2]
#output y= TO N AX AX N TO