Ruby Case Examples: Ranges, Strings and RegexpUse the case statement. Match values, and ranges of values, with this statement.
dot net perls

Case. A case-statement tests values. It matches the value of a variable against ranges and other values. It yields a specified value. It influences control flow.

Ranges, expressions. Case is an alternative syntax form to the if-statement. We use ranges, strings and numbers with cases. We can assign or return the case's result.

Case example. We use a case in a method. The method test() returns the value from a case-statement evaluation. It returns the strings Low, Medium or High based on the parameter.

Ranges We use numeric ranges in the when-statements. To specify a range, separate two numbers with two periods.

Else Else optionally comes at the end. If no other ranges or values match, the else-statement is reached. This is a default.

Ruby program that uses case-statement
# Test method. def test(quality) # Return a case. return case quality when 0..2 then "Low" when 3..5 then "Medium" when 6..8 then "High" else "Invalid" end end # Call test method. print test(0), "\n" print test(4), "\n" print test(8), "\n" print test(-1), "\n"
Low Medium High Invalid

Numbers. A case requires no ranges. In this example, we use simple number "when" statements. For example, we return 400 when the value equals 4.

Note The case statement evaluates and its result is stored in the "result" variable's memory location.

Expression We use the case as an expression in this program, one that is evaluated to return a value.

Tip In Ruby, expressions and statements are often interchangeable. This makes constructs like "case" useful in many contexts.

Ruby program that uses case, no ranges
value = 5 # Use case with numbers, no ranges. result = case value when 4 then 400 when 5 then 500 when 6 then 600 else 0 end # Display input and output. puts value puts result
5 500

String. A string can be used in a case. In this example, we use a string in a case expression, and then assign an integer to the result. The case evaluates to the value 2.

Also This case expression uses an else-statement. If the value of "name" is not matched, the value 3 is returned by this expression.

Ruby program that uses string case
# The value. name = "sam" # Assign to result of string case expression. id = case name when "edna" then 0 when "fred" then 1 when "sam" then 2 else 3 end # Display result. puts id

When. This can have multiple values in it. Here we see a when statement that matches if the variable equals 100 or 200. This syntax form is a good choice when a range is unnecessary.

Ruby program that uses when, multiple values
apartment = 200 case apartment when 100, 200 # Has two possible matching values. puts "100 or 200" when 0 puts "Zero" end
100 or 200

Regexp. A case can use Regexp in the when statements. Here we use a regular expression to test first letters. Any regular expression can be used. And we can even capture groups.

Here The case block detects that the word "Alexandria" starts with the letter "A." The Regexp is described.

Ruby program that uses Regexp, case
value = "alexandria" # Use case with regular expressions. case value when /^a/ puts "Starts with letter A" when /^b/ puts "Starts with B" end
Starts with letter A

Pattern details:
^a String starts with a lowercase letter A. ^b String starts with a "b".

Regexp, captures. This example combines many constructs in Ruby. We use an iterator (each) over a string array. We then use a case-statement with regular expressions.

Tip After a Regexp matches a value in a case, its groups are stored in a special variable $1. We get the captured value there.

Tip 2 We can also directly display the value of $1 in a puts call with the code #$1. This helps us develop a simple text parser.

Ruby program that uses case, Regexp, captures
# An array of strings. values = ["value 100", "string box"] # Loop over strings. values.each do |value| # Use regular expression in case-statement. # ... Use capturing. case value when /value (\d+)/ # Access the capture from $1. argument = $1 # Use format string to display argument. puts "Value argument = %s" % argument when /string (.+)/ # Directly display captured value. puts "String argument = #$1" end end
Value argument = 100 String argument = box

Case benchmark. In this test, case has no performance advantage. It is many times slower than an equivalent if-statement. This depends on the data being tested.

Version 1 In this version of the logic, we assign a variable to the result of a case statement.

Version 2 Here, we assign a variable using an if-statement instead of the case-statement.

Result To boost performance, it is sometimes helpful to replace cases with if-statements.

Ruby program that times case-statement
count = 100000 n1 = Time.now.usec x = 0 v = 5 # Version 1: assign a variable with a case-statement. count.times do x = case v when 0..1 then 1 when 2..3 then 2 when 4..6 then 3 else 0 end end puts x n2 = Time.now.usec # Version 2: assign a variable with an if-statement. count.times do if v >= 0 && v <= 1 x = 1 elsif v >= 2 && v <= 3 x = 2 elsif v >= 4 && v <= 6 x = 3 else x = 0 end end puts x n3 = Time.now.usec # Times. puts ((n2 - n1) / 1000) puts ((n3 - n2) / 1000)
3 3 92 ms, case-statement 15 ms, if-elsif-else statements

A summary. Case is a selection statement. It is similar, conceptually, to switch statements and to select-case statements in other languages.

Case has advantages. Its syntax is clear and easy to read. It also has limitations—it may evaluate slower. We used a case-statement in a method.

© 2007-2021 sam allen. send bug reports to info@dotnetperls.com.