Range

Class

A Range represents an interval—a set of values with a beginning and an end. Ranges may be constructed using the s..e and s...e literals, or with Range::new. Ranges constructed using .. run from the beginning to the end inclusively. Those created using ... exclude the end value. When used as an iterator, ranges return each value in the sequence.

(-1..-5).to_a      #=> []
(-5..-1).to_a      #=> [-5, -4, -3, -2, -1]
('a'..'e').to_a    #=> ["a", "b", "c", "d", "e"]
('a'...'e').to_a   #=> ["a", "b", "c", "d"]

Beginless/Endless Ranges

A “beginless range” and “endless range” represents a semi-infinite range. Literal notation for a beginless range is:

(..1)
# or
(...1)

Literal notation for an endless range is:

(1..)
# or similarly
(1...)

Which is equivalent to

(1..nil)  # or similarly (1...nil)
Range.new(1, nil) # or Range.new(1, nil, true)

Beginless/endless ranges are useful, for example, for idiomatic slicing of arrays:

[1, 2, 3, 4, 5][...2]   # => [1, 2]
[1, 2, 3, 4, 5][2...]   # => [3, 4, 5]

Some implementation details:

  • begin of beginless range and end of endless range are nil;

  • each of beginless range raises an exception;

  • each of endless range enumerates infinite sequence (may be useful in combination with Enumerable#take_while or similar methods);

  • (1..) and (1...) are not equal, although technically representing the same sequence.

Custom Objects in Ranges

Ranges can be constructed using any objects that can be compared using the <=> operator. Methods that treat the range as a sequence (each and methods inherited from Enumerable) expect the begin object to implement a succ method to return the next object in sequence. The step and include? methods require the begin object to implement succ or to be numeric.

In the Xs class below both <=> and succ are implemented so Xs can be used to construct ranges. Note that the Comparable module is included so the == method is defined in terms of <=>.

class Xs                # represent a string of 'x's
  include Comparable
  attr :length
  def initialize(n)
    @length = n
  end
  def succ
    Xs.new(@length + 1)
  end
  def <=>(other)
    @length <=> other.length
  end
  def to_s
    sprintf "%2d #{inspect}", @length
  end
  def inspect
    'x' * @length
  end
end

An example of using Xs to construct a range:

r = Xs.new(3)..Xs.new(6)   #=> xxx..xxxxxx
r.to_a                     #=> [xxx, xxxx, xxxxx, xxxxxx]
r.member?(Xs.new(5))       #=> true
Class Methods

json_create(object)
::

Deserializes JSON string by constructing new Range object with arguments a serialized by to_json.

Range.new(begin, end, exclude_end=false) → rng
::

Constructs a range using the given begin and end. If the exclude_end parameter is omitted or is false, the range will include the end object; otherwise, it will be excluded.

Instance Methods

rng.step(n=1) {| obj | block } → rng

rng.step(n=1) → an_enumerator

rng.step(n=1) → an_arithmetic_sequence

rng % n → an_enumerator

rng % n → an_arithmetic_sequence
#

Iterates over the range, passing each nth element to the block. If begin and end are numeric, n is added for each iteration. Otherwise step invokes succ to iterate through range elements.

If no block is given, an enumerator is returned instead. Especially, the enumerator is an Enumerator::ArithmeticSequence if begin and end of the range are numeric.

range = Xs.new(1)..Xs.new(10)
range.step(2) {|x| puts x}
puts
range.step(3) {|x| puts x}

produces:

 1 x
 3 xxx
 5 xxxxx
 7 xxxxxxx
 9 xxxxxxxxx

 1 x
 4 xxxx
 7 xxxxxxx
10 xxxxxxxxxx

See Range for the definition of class Xs.

rng == obj → true or false
#

Returns true only if obj is a Range, has equivalent begin and end items (by comparing them with ==), and has the same exclude_end? setting as the range.

(0..2) == (0..2)            #=> true
(0..2) == Range.new(0,2)    #=> true
(0..2) == (0...2)           #=> false

rng === obj → true or false
#

Returns true if obj is between begin and end of range, false otherwise (same as cover?). Conveniently, === is the comparison operator used by case statements.

case 79
when 1..50   then   puts "low"
when 51..75  then   puts "medium"
when 76..100 then   puts "high"
end
# Prints "high"

case "2.6.5"
when ..."2.4" then puts "EOL"
when "2.4"..."2.5" then puts "maintenance"
when "2.5"..."2.7" then puts "stable"
when "2.7".. then puts "upcoming"
end
# Prints "stable"

as_json(*)
#

Returns a hash, that will be turned into a JSON object and represent this object.

rng.begin → obj
#

Returns the object that defines the beginning of the range.

(1..10).begin   #=> 1

rng.bsearch {|obj| block } → value
#

By using binary search, finds a value in range which meets the given condition in O(log n) where n is the size of the range.

You can use this method in two use cases: a find-minimum mode and a find-any mode. In either case, the elements of the range must be monotone (or sorted) with respect to the block.

In find-minimum mode (this is a good choice for typical use case), the block must return true or false, and there must be a value x so that:

  • the block returns false for any value which is less than x, and

  • the block returns true for any value which is greater than or equal to x.

If x is within the range, this method returns the value x. Otherwise, it returns nil.

ary = [0, 4, 7, 10, 12]
(0...ary.size).bsearch {|i| ary[i] >= 4 } #=> 1
(0...ary.size).bsearch {|i| ary[i] >= 6 } #=> 2
(0...ary.size).bsearch {|i| ary[i] >= 8 } #=> 3
(0...ary.size).bsearch {|i| ary[i] >= 100 } #=> nil

(0.0...Float::INFINITY).bsearch {|x| Math.log(x) >= 0 } #=> 1.0

In find-any mode (this behaves like libc’s bsearch(3)), the block must return a number, and there must be two values x and y (x <= y) so that:

  • the block returns a positive number for v if v < x,

  • the block returns zero for v if x <= v < y, and

  • the block returns a negative number for v if y <= v.

This method returns any value which is within the intersection of the given range and x…y (if any). If there is no value that satisfies the condition, it returns nil.

ary = [0, 100, 100, 100, 200]
(0..4).bsearch {|i| 100 - ary[i] } #=> 1, 2 or 3
(0..4).bsearch {|i| 300 - ary[i] } #=> nil
(0..4).bsearch {|i|  50 - ary[i] } #=> nil

You must not mix the two modes at a time; the block must always return either true/false, or always return a number. It is undefined which value is actually picked up at each iteration.

range.count → int

range.count(item) → int

range.count { |obj| block } → int
#

Identical to Enumerable#count, except it returns Infinity for endless ranges.

rng.cover?(obj) → true or false

rng.cover?(range) → true or false
#

Returns true if obj is between the begin and end of the range.

This tests begin <= obj <= end when exclude_end? is false and begin <= obj < end when exclude_end? is true.

If called with a Range argument, returns true when the given range is covered by the receiver, by comparing the begin and end values. If the argument can be treated as a sequence, this method treats it that way. In the specific case of (a..b).cover?(c...d) with a <= c && b < d, the end of the sequence must be calculated, which may exhibit poor performance if c is non-numeric. Returns false if the begin value of the range is larger than the end value. Also returns false if one of the internal calls to <=> returns nil (indicating the objects are not comparable).

("a".."z").cover?("c")  #=> true
("a".."z").cover?("5")  #=> false
("a".."z").cover?("cc") #=> true
("a".."z").cover?(1)    #=> false
(1..5).cover?(2..3)     #=> true
(1..5).cover?(0..6)     #=> false
(1..5).cover?(1...6)    #=> true

rng.each {| i | block } → rng

rng.each → an_enumerator
#

Iterates over the elements of range, passing each in turn to the block.

The each method can only be used if the begin object of the range supports the succ method. A TypeError is raised if the object does not have succ method defined (like Float).

If no block is given, an enumerator is returned instead.

(10..15).each {|n| print n, ' ' }
# prints: 10 11 12 13 14 15

(2.5..5).each {|n| print n, ' ' }
# raises: TypeError: can't iterate from Float

rng.end → obj
#

Returns the object that defines the end of the range.

(1..10).end    #=> 10
(1...10).end   #=> 10

rng.entries → array
#
An alias for to_a

rng.eql?(obj) → true or false
#

Returns true only if obj is a Range, has equivalent begin and end items (by comparing them with eql?), and has the same exclude_end? setting as the range.

(0..2).eql?(0..2)            #=> true
(0..2).eql?(Range.new(0,2))  #=> true
(0..2).eql?(0...2)           #=> false

rng.exclude_end? → true or false
#

Returns true if the range excludes its end value.

(1..5).exclude_end?     #=> false
(1...5).exclude_end?    #=> true

rng.first → obj

rng.first(n) → an_array
#

Returns the first object in the range, or an array of the first n elements.

(10..20).first     #=> 10
(10..20).first(3)  #=> [10, 11, 12]

rng.hash → integer
#

Compute a hash-code for this range. Two ranges with equal begin and end points (using eql?), and the same exclude_end? value will generate the same hash-code.

See also Object#hash.

rng.include?(obj) → true or false
#
An alias for member?

rng.inspect → string
#

Convert this range object to a printable form (using inspect to convert the begin and end objects).

rng.last → obj

rng.last(n) → an_array
#

Returns the last object in the range, or an array of the last n elements.

Note that with no arguments last will return the object that defines the end of the range even if exclude_end? is true.

(10..20).last      #=> 20
(10...20).last     #=> 20
(10..20).last(3)   #=> [18, 19, 20]
(10...20).last(3)  #=> [17, 18, 19]

rng.max → obj

rng.max {| a,b | block } → obj

rng.max(n) → obj

rng.max(n) {| a,b | block } → obj
#

Returns the maximum value in the range. Returns nil if the begin value of the range larger than the end value. Returns nil if the begin value of an exclusive range is equal to the end value.

Can be given an optional block to override the default comparison method a <=> b.

(10..20).max    #=> 20

rng.member?(obj) → true or false
#

Returns true if obj is an element of the range, false otherwise.

("a".."z").include?("g")   #=> true
("a".."z").include?("A")   #=> false
("a".."z").include?("cc")  #=> false

If you need to ensure obj is between begin and end, use cover?

("a".."z").cover?("cc")  #=> true

If begin and end are numeric, include? behaves like cover?

(1..3).include?(1.5) # => true

rng.min → obj

rng.min {| a,b | block } → obj

rng.min(n) → array

rng.min(n) {| a,b | block } → array
#

Returns the minimum value in the range. Returns nil if the begin value of the range is larger than the end value. Returns nil if the begin value of an exclusive range is equal to the end value.

Can be given an optional block to override the default comparison method a <=> b.

(10..20).min    #=> 10

rng.minmax → [obj, obj]

rng.minmax {| a,b | block } → [obj, obj]
#

Returns a two element array which contains the minimum and the maximum value in the range.

Can be given an optional block to override the default comparison method a <=> b.

rng.size → num
#

Returns the number of elements in the range. Both the begin and the end of the Range must be Numeric, otherwise nil is returned.

(10..20).size    #=> 11
('a'..'z').size  #=> nil
(-Float::INFINITY..Float::INFINITY).size #=> Infinity

rng.step(n=1) {| obj | block } → rng

rng.step(n=1) → an_enumerator

rng.step(n=1) → an_arithmetic_sequence

rng % n → an_enumerator

rng % n → an_arithmetic_sequence
#

Iterates over the range, passing each nth element to the block. If begin and end are numeric, n is added for each iteration. Otherwise step invokes succ to iterate through range elements.

If no block is given, an enumerator is returned instead. Especially, the enumerator is an Enumerator::ArithmeticSequence if begin and end of the range are numeric.

range = Xs.new(1)..Xs.new(10)
range.step(2) {|x| puts x}
puts
range.step(3) {|x| puts x}

produces:

 1 x
 3 xxx
 5 xxxxx
 7 xxxxxxx
 9 xxxxxxxxx

 1 x
 4 xxxx
 7 xxxxxxx
10 xxxxxxxxxx

See Range for the definition of class Xs.

rng.to_a → array
#

Returns an array containing the items in the range.

(1..7).to_a  #=> [1, 2, 3, 4, 5, 6, 7]
(1..).to_a   #=> RangeError: cannot convert endless range to an array

to_json(*args)
#

Stores class name (Range) with JSON array of arguments a which include first (integer), last (integer), and exclude_end? (boolean) as JSON string.

rng.to_s → string
#

Convert this range object to a printable form (using to_s to convert the begin and end objects).