Scala Cookbook

1.5. Processing a String One Character at a Time

Problem

You want to iterate through each character in a string, performing an operation on each character as you traverse the string.

Solution

Depending on your needs and preferences, you can use the map or foreach methods, a for loop, or other approaches. Here’s a simple example of how to create an uppercase string from an input string, using map:

scala> val upper = "hello, world".map(c => c.toUpper)
upper: String = HELLO, WORLD

As you’ll see in many examples throughout this book, you can shorten that code using the magic of Scala’s underscore character:

scala> val upper = "hello, world".map(_.toUpper)
upper: String = HELLO, WORLD

With any collection—such as a sequence of characters in a string—you can also chain collection methods together to achieve a desired result. In the following example, the filter method is called on the original String to create a new String with all occurrences of the lowercase letter “L” removed. That String is then used as input to the map method to convert the remaining characters to uppercase:

scala> val upper = "hello, world".filter(_ != 'l').map(_.toUpper)
upper: String = HEO, WORD

When you first start with Scala, you may not be comfortable with the map method, in which case you can use Scala’s for loop to achieve the same result. This example shows another way to print each character:

scala> for (c <- "hello") println(c)
h
e
l
l
o

To write a for loop to work like a map method, add a yield statement to the end ...