Scala Regex, R Examples: findFirstMatchIn

Use the Regex class to match patterns. Call findFirstMatchIn and other methods.

R, Regex. Some text operations are simple. We compare a string. We test a character. But for complex things, a Regex provides more power and is more effective.

With r, a function on strings, we create a regular expression from a string (a pattern). We then invoke methods that find matches on that pattern.

FindFirstMatchIn example. Here we create a Regex object from a pattern string with r(). Please note how we specify the Regex pattern—we use three quotes, which is a raw string literal.

For: We use a for-loop over the strings in our list. We call findFirstMatchIn on each string.

For String

Result: The Regex matches strings that have one or more digits followed by the word "pounds."

Scala program that uses r, findFirstMatchIn // Get Regex from this string. val test = """\d* pounds""".r // A list of strings to match. val data = List("20 pounds", "5 pounds", "Error") // Loop over strings in the list. for (v <- data) { // Try to match the strings. val result = test.findFirstMatchIn(v) if (result.isDefined) { println(v + " = true") } else { println(v + " = false") } } Output 20 pounds = true 5 pounds = true Error = false

Groups. These help us label and access parts of a string. We use parentheses around the parts of our Regex we want to be placed in groups. And we pass group names to the r() method.

Result: We test isDefined to see if the option has an inner value. We use "get" to access the inner Regex.

And: We call the group() function, with string arguments, to access the named groups from our Regex object.

Scala program that uses Regex groups // An example string. val animals = "cat and dog" // Match words surrounding "and" and give them group names. val result = """(\w+) and (\w+)""".r( "animal1", "animal2").findFirstMatchIn(animals) // See if match occurred. if (result.isDefined) { // Get the Regex. val regex = result.get // Get named groups and display them. val animal1 = regex.group("animal1") val animal2 = regex.group("animal2") println(animal1) println(animal2) } Output cat dog

FindAllIn. This program uses findAllIn to get a MatchIterator from a Regex. Here we match all substrings in the string that start with a lowercase "a" or "b" and are followed by 2 digits.

For: We use a for-in loop to iterate over the results of MatchIterator. We access and print each string match.

Scala program that uses findAllIn // Contains space-separated ID codes. val ids = "a_1 a21 a31 b21 b_3 c10" // Match all occurrences starting with "a" or "b" and with 2 digits. val result = """[ab]\d\d""".r.findAllIn(ids) // Iterate over our result. // ... This accesses the Regex.MatchIterator. for (r <- result) { println(r) } Output a21 a31 b21

A summary. Scala provides pattern matching for variables with the "match" keyword. But for text, we can use regular expressions. We create them with the r() function.Match

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Scala Regex, R Examples: findFirstMatchIn

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