R Language Regular Expressions (regex) Escaping characters in R regex patterns
Example
Since both R and regex share the escape character ,"\", building correct patterns for grep, sub, gsub or any other function that accepts a pattern argument will often need pairing of backslashes. If you build a three item character vector in which one items has a linefeed, another a tab character and one neither, and hte desire is to turn either the linefeed or the tab into 4-spaces then a single backslash is need for the construction, but tpaired backslashes for matching:
x <- c( "a\nb", "c\td", "e f")
x # how it's stored
# [1] "a\nb" "c\td" "e f"
cat(x) # how it will be seen with cat
#a
#b c d e f
gsub(patt="\\n|\\t", repl=" ", x)
#[1] "a b" "c d" "e f"
Note that the pattern argument (which is optional if it appears first and only needs partial spelling) is the only argument to require this doubling or pairing. The replacement argument does not require the doubling of characters needing to be escaped. If you wanted all the linefeeds and 4-space occurrences replaces with tabs it would be:
gsub("\\n| ", "\t", x)
#[1] "a\tb" "c\td" "e\tf"
