Regular expressions

Suppose you find that there are commas separating every third digit of the numbers in a numeric column. How would you remove them? Or suppose you needed to strip a currency symbol from values in columns that hold monetary values so that you can compute with them as numbers. These, and vastly more complicated text transformations, can be performed using a most powerful tool, regular expressions.

What are regular expressions?

Regular expressions (or regexes, as it is commonly abbreviated) is a formal grammar for describing patterns in text/strings. In general purpose programming languages, it is often used for things like verifying user input, but it is most often used in the context of statistical programming to transform the textual representation of raw data. Regular expressions are—at once—the plural form of a single regular expression, a powerful tool, an idea, and a language for describing patterns in text.

You might ask yourself: How do I work with this? You might first...