How to format numbers and currency in Scala

Scala FAQ: How can I format numbers and currency in Scala, such as to control the number of decimal places and commas in the values, typically for printed output.

Basic formatting

For basic number formatting, use the f string interpolator shown in Recipe 1.4 of the Scala Cookbook, “Substituting Variables into Strings”:

scala> val pi = scala.math.Pi
pi: Double = 3.141592653589793

scala> println(f"$pi%1.5f")
3.14159

A few more examples demonstrate the technique:

scala> f"$pi%1.5f"
res0: String = 3.14159

scala> f"$pi%1.2f"
res1: String = 3.14

scala> f"$pi%06.2f"
res2: String = 003.14

The 'format' method

If you’re using a version of Scala prior to 2.10, or prefer the explicit use of the format method, you can write the code like this instead:

scala> "%06.2f".format(pi)
res3: String = 003.14

Handling commas in numbers

A simple way to add commas is to use the getIntegerInstance method of the java.text.NumberFormat class:

scala> val formatter = java.text.NumberFormat.getIntegerInstance
formatter: java.text.NumberFormat = java.text.DecimalFormat@674dc

scala> formatter.format(10000)
res0: String = 10,000

scala> formatter.format(1000000)
res1: String = 1,000,000

Setting the locale

You can also set a locale with the getIntegerInstance method:

scala> val locale = new java.util.Locale("de", "DE")
locale: java.util.Locale = de_DE

scala> val formatter = java.text.NumberFormat.getIntegerInstance(locale)
formatter: java.text.NumberFormat = java.text.DecimalFormat@674dc

scala> formatter.format(1000000)
res2: String = 1.000.000

Formatting floating-point numbers

You can handle floating-point values with a formatter returned by getInstance:

scala> val formatter = java.text.NumberFormat.getInstance
formatter: java.text.NumberFormat = java.text.DecimalFormat@674dc

scala> formatter.format(10000.33)
res0: String = 10,000.33

Formatting currency

For currency output, use the getCurrencyInstance formatter:

scala> val formatter = java.text.NumberFormat.getCurrencyInstance
formatter: java.text.NumberFormat = java.text.DecimalFormat@67500

scala> println(formatter.format(123.456789))
$123.46

scala> println(formatter.format(1234.56789))
$1,234.57

scala> println(formatter.format(12345.6789))
$12,345.68

scala> println(formatter.format(123456.789))
$123,456.79

Formatting international currency

This approach handles international currency:

scala> import java.util.{Currency, Locale}
import java.util.{Currency, Locale}

scala> val de = Currency.getInstance(new Locale("de", "DE"))
de: java.util.Currency = EUR

scala> formatter.setCurrency(de)

scala> println(formatter.format(123456.789))
EUR123,456.79

Discussion

This recipe falls back to the Java approach for printing currency and other formatted numeric fields, though of course the currency solution depends on how you handle currency in your applications. In my work as a consultant, I’ve seen most companies handle currency using the Java BigDecimal class, and others create their own custom currency classes, which are typically wrappers around BigDecimal.

See Also

• My printf cheat sheet
• The Joda Money library is a Java library for handling currency
• JSR 354: Money and Currency API, is also being developed in the Java Community Process. See jcp.org for more information.