> For the complete documentation index, see [llms.txt](https://ondrej-kvasnovsky-2.gitbook.io/handbook-of-hidden-data-scientist/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://ondrej-kvasnovsky-2.gitbook.io/handbook-of-hidden-data-scientist/cleaning_data/regular_expressions.md).

# Regular Expressions

In many cases, first we will have to develop a regular expression. We can use <http://www.regexr.com> to do that.

Lets say we created this regular expression `want|develop` that will find rows where there is "want" or "develop" words.

We can use regular expressions with `grep`, `grepl`, `sub`, `strsplit`, `regexpr`, `gregexpr` and `gsub` functions.

## [grep](http://stat.ethz.ch/R-manual/R-devel/library/base/html/grep.html) function

```r
> text <- "We want to develop new regular expression."
> grep("want|develop", text, value=TRUE)

[1] "We want to develop new regular expression."
```

More about [regular expressions in R](http://www.regular-expressions.info/rlanguage.html) or [here](http://stat.ethz.ch/R-manual/R-devel/library/base/html/regex.html).