Take the 2-minute tour ×

I have a large text vector I would like to search for a particular character or phrase. Regular expressions are taking forever. How do I search it quickly?

Sample data:

R <- 10^7
garbage <- replicate( R, paste0(sample(c(letters[1:5]," "),10,replace=TRUE),collapse="") )
share|improve this question

2 Answers 2

up vote 5 down vote accepted

If you do need regular expressions, you can generally get a performance increase over the default regular expression engine by using the PCRE library (by setting perl=TRUE). There are other performance tips in ?grep:

Performance considerations:

If you are doing a lot of regular expression matching, including on very long strings, you will want to consider the options used. Generally PCRE will be faster than the default regular expression engine, and ‘fixed = TRUE’ faster still (especially when each pattern is matched only a few times).


If you can make use of ‘useBytes = TRUE’, the strings will not be checked before matching, and the actual matching will be faster. Often byte-based matching suffices in a UTF-8 locale since byte patterns of one character never match part of another.

share|improve this answer
Cool. Presumably there are tricks with factors that could work as well if you have lots of repeated vectors.... –  Ari B. Friedman Oct 18 '13 at 23:17

There's no need for regular expressions here, and their power comes with a computational cost.

You can turn off regular expression parsing in any of the regex functions in R with the ,fixed=TRUE argument. Speed gains result:

m <- microbenchmark( 
    grep( " ", garbage, fixed=TRUE ),
    grep( " ", garbage )
Unit: milliseconds
                             expr       min        lq   median        uq      max neval
 grep(" ", garbage, fixed = TRUE)  491.5634  497.1309  499.109  503.3009 1128.643   100
               grep(" ", garbage) 1786.8500 1801.9837 1810.294 1825.2755 3620.346   100
share|improve this answer

Your Answer


