Scala Cookbook

1.8. Extracting Parts of a String That Match Patterns

Problem

You want to extract one or more parts of a string that match the regular-expression patterns you specify.

Solution

Define the regular-expression patterns you want to extract, placing parentheses around them so you can extract them as “regular-expression groups.” First, define the desired pattern:

val pattern = "([0-9]+) ([A-Za-z]+)".r

Next, extract the regex groups from the target string:

val pattern(count, fruit) = "100 Bananas"

This code extracts the numeric field and the alphabetic field from the given string as two separate variables, count and fruit, as shown in the Scala REPL:

scala> val pattern = "([0-9]+) ([A-Za-z]+)".r
pattern: scala.util.matching.Regex = ([0-9]+) ([A-Za-z]+)

scala> val pattern(count, fruit) = "100 Bananas"
count: String = 100
fruit: String = Bananas

Discussion

The syntax shown here may feel a little unusual because it seems like you’re defining pattern as a val field twice, but this syntax is more convenient and readable in a real-world example.

Imagine you’re writing the code for a search engine like Google, and you want to let people search for movies using a wide variety of phrases. To be really convenient, you’ll let them type any of these phrases to get a listing of movies near Boulder, Colorado:

"movies near 80301"
"movies 80301"
"80301 movies"
"movie: 80301"
"movies: 80301"
"movies near boulder, co"
"movies near boulder, colorado"

One way you can allow all these phrases to be used is to define a series ...