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.
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.
# Test method.
Ruby program that uses case-statement
# Return a case.
# Call test method.
print test(0), "\n"
print test(4), "\n"
print test(8), "\n"
print test(-1), "\n"
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
when 4 then 400
when 6 then 600
# Display input and output.
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.
# The value.
Ruby program that uses string case
name = "sam"
# Assign to result of string case expression.
id = case
when "edna" then 0
when "fred" then 1
# Display result.
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
# Has two possible matching values.
puts "100 or 200"
100 or 200
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.
puts "Starts with letter A"
puts "Starts with B"
Starts with letter A
^a String starts with a lowercase letter A.
^b String starts with a "b".
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.
# An array of strings.
Ruby program that uses case, Regexp, captures
values = ["value 100", "string box"]
# Loop over strings.
values.each do |value|
# Use regular expression in case-statement.
# ... Use capturing.
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"
Value argument = 100
String argument = box
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.
x = case
when 0..1 then 1
when 2..3 then 2
when 4..6 then 3
n2 = Time.now.usec
# Version 2: assign a variable with an if-statement.
v >= 0 && v <= 1
x = 1
elsif v >= 2 && v <= 3
x = 2
elsif v >= 4 && v <= 6
x = 3
x = 0
n3 = Time.now.usec
puts ((n2 - n1) / 1000)
puts ((n3 - n2) / 1000)
, 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 email@example.com.