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"]
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.
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
Iterates over the range, passing each n
th 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.
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
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"
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.
Identical to Enumerable#count
, except it returns Infinity for endless ranges.
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
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
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
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
Returns true
if the range excludes its end value.
(1..5).exclude_end? #=> false (1...5).exclude_end? #=> true
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]
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
.
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
Convert this range object to a printable form (using inspect
to convert the begin and end objects).
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]
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
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
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
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
.
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.
Iterates over the range, passing each n
th 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.
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
Convert this range object to a printable form (using to_s
to convert the begin and end objects).