regexplain

regexplain is an RStudio addin that helps you interactively build up your regex expressions. Inspired by RegExr and stringr::str_view.

Installation

Installation is easy with devtools:

devtools::install_github("gadenbuie/regexplain")

Status

Mostly working, but there may be issues or future changes.

I would love your help testing this, feel free to send me your feedback on Twitter at @grrrck or through the issue tracker.

RStudio Addin

regexplain screencast

The main feature of this package is the RStudio Addin Regexplain Selection. Just select the text or object containing text (such as the variable name of a vector or a data.frame column) and run Regexplain Selection from the RStudio Addins dropdown.

The addin will open an interface with 4 panes where you can

• edit the text you’ve imported
• build up a regex expression and interactively see it applied to your text
• test the output of common string matching functions from base and stringr
• and refer to a helpful cheatsheet

The panes of regexplain

When you’re done, click on the Send Regex to Console to send your regex expression to… the console!

> regex <- "(is|were|was) ([[:alpha:]]+) ([[:alpha:]]+)"

Additional Addins

There are two more addins. Regexplain File lets you import the text lines from a file containing the text you want to process with regular expressions. Regexplain Cheatsheet opens the help page in the Viewer pane without blocking your current R session.

View regex results without the interactivity

regexplain also provides the function view_regex() that you can use as a stringr::str_view() replacement. In addition to highlighting matched portions of the text, view_regex() also colorizes groups and attemps to colorize the regex expression itself as well.

text <- c("breakfast=eggs;lunch=pizza",
          "breakfast=bacon;lunch=spaghetti", 
          "no food here")
pattern <- "((\\w+)=)(\\w+).+(ch=s?p)"

view_regex(text, pattern)

Example view_regex(text, pattern).

t_nested <- "anestedgroupwithingroupexample"
r_nested <- "(a(nested)(group(within(group))(example)))"
view_regex(t_nested, r_nested)

Example of nested groups

Known Issues and Future Work

Regular expressions are nothing if not a collection of corner cases. Trying to pass regular expressions through Shiny and HTML inputs is a bit of a labrynth. For now, assume any issues or oddities you experience with this addin are entirely my fault and have nothing to do with the fine packages this addin is built on. If you do find an issue, please file an issue.

Things I know are wonky

• Things get weird when regular text is surrounded by capture groups, i.e. "(\w+) not grouped (\w+)".

• view_regex() colorizes non-capture groups. I forgot about them when building that feature, I’ll get back to it.

Notes

• I’ve set up this app so that most escape sequences don’t need to be escaped. For example, you can enter \w, whereas in R this would need to be stored as "\\w". The regex returned by the gadget will include the double backslash. In these cases the text input is not escaped by Shiny.

  Unicode and hex escape characters also do not need to be escaped, thanks to stringi::stri_unescape_unicode(). Here, "\u" is escaped by Shiny so I had to make sure they are unescaped. The list of escaped characters that get unescaped is "\\u|\\x|\\N|\\a|\\o", please let me know if you find any others that should be on this list.

Planned improvements

• I may add stringi functions to the list of available functions in the Output tab.

• I would like to add the regex/function options for the functions in the Output tab, similar to the options present in the Regex tab.