Re: [R] regular expression in gsub() for strings with leading backslash

From: Mike Miller <>
Date: Fri, 29 Apr 2011 20:46:06 -0500 (CDT)

On Fri, 29 Apr 2011, Duncan Murdoch wrote:

> On 29/04/2011 7:41 PM, Miao wrote:
>> Can anyone help on gsub() in R? I have a string like something below, and
>> wanted to delete all the strings with leading backslash, including
>> "\xa0On",
>> "\023, "\xab", and many others. How should I write a regular expression
>> pattern in gsub()? I don't care how many characters following backslash.
> If those are R strings, none of them contain a backslash. In R, a backslash
> would always be printed as \\.
> \x is the introduction to a hexadecimal encoding for a character; the next
> two characters show the hex digits. So your first string contains a single
> character \xa0, the third one contains \xab, and so on.
> The \023 is an octal encoding for a single character.

If we were dealing with a leading backslash, I guess this would do it:

gsub("^\\\\.*", "", txt)

R would display a double backslash, but I believe that represents a single backslash. So if the string were saved using write.table, say, only a single backslash would be stored.

> a <- "\\This is a string."
> a

[1] "\\This is a string."
> gsub("^\\\\", "", a)

[1] "This is a string."
> a

[1] "\\This is a string."
> gsub("^\\\\.*", "", a)

[1] ""
> gsub("^\\\\.*", "", c(a,"Another string","\\more"))
[1] "" "Another string" ""
> write.table(a, file="a.txt", quote=F, row.names=F, col.names=F)

$ cat a.txt
\This is a string.

Apparently this is not what the OP really wanted. The OP probably wanted to remove characters that were not from the regular ASCII set.


Michael B. Miller, Ph.D.
Minnesota Center for Twin and Family Research
Department of Psychology
University of Minnesota

______________________________________________ mailing list
PLEASE do read the posting guide
and provide commented, minimal, self-contained, reproducible code.
Received on Sat 30 Apr 2011 - 01:50:50 GMT

Archive maintained by Robert King, hosted by the discipline of statistics at the University of Newcastle, Australia.
Archive generated by hypermail 2.2.0, at Sat 30 Apr 2011 - 04:00:36 GMT.

Mailing list information is available at Please read the posting guide before posting to the list.

list of date sections of archive