Enumerable

Returns whether every element meets a given criterion.

If self has no element, returns true and argument or block are not used.

With no argument and no block, returns whether every element is truthy:

(1..4).all?           # => true
%w[a b c d].all?      # => true
[1, 2, nil].all?      # => false
['a','b', false].all? # => false
[].all?               # => true

With argument pattern and no block, returns whether for each element element, pattern === element:

(1..4).all?(Integer)                 # => true
(1..4).all?(Numeric)                 # => true
(1..4).all?(Float)                   # => false
%w[bar baz bat bam].all?(/ba/)       # => true
%w[bar baz bat bam].all?(/bar/)      # => false
%w[bar baz bat bam].all?('ba')       # => false
{foo: 0, bar: 1, baz: 2}.all?(Array) # => true
{foo: 0, bar: 1, baz: 2}.all?(Hash)  # => false
[].all?(Integer)                     # => true

With a block given, returns whether the block returns a truthy value for every element:

(1..4).all? {|element| element < 5 }                    # => true
(1..4).all? {|element| element < 4 }                    # => false
{foo: 0, bar: 1, baz: 2}.all? {|key, value| value < 3 } # => true
{foo: 0, bar: 1, baz: 2}.all? {|key, value| value < 2 } # => false

Related: any?, none? one?.

Returns whether any element meets a given criterion.

If self has no element, returns false and argument or block are not used.

With no argument and no block, returns whether any element is truthy:

(1..4).any?          # => true
%w[a b c d].any?     # => true
[1, false, nil].any? # => true
[].any?              # => false

With argument pattern and no block, returns whether for any element element, pattern === element:

[nil, false, 0].any?(Integer)        # => true
[nil, false, 0].any?(Numeric)        # => true
[nil, false, 0].any?(Float)          # => false
%w[bar baz bat bam].any?(/m/)        # => true
%w[bar baz bat bam].any?(/foo/)      # => false
%w[bar baz bat bam].any?('ba')       # => false
{foo: 0, bar: 1, baz: 2}.any?(Array) # => true
{foo: 0, bar: 1, baz: 2}.any?(Hash)  # => false
[].any?(Integer)                     # => false

With a block given, returns whether the block returns a truthy value for any element:

(1..4).any? {|element| element < 2 }                    # => true
(1..4).any? {|element| element < 1 }                    # => false
{foo: 0, bar: 1, baz: 2}.any? {|key, value| value < 1 } # => true
{foo: 0, bar: 1, baz: 2}.any? {|key, value| value < 0 } # => false

Related: all?, none?, one?.

Returns an enumerator object generated from this enumerator and given enumerables.

e = (1..3).chain([4, 5])
e.to_a #=> [1, 2, 3, 4, 5]

Each element in the returned enumerator is a 2-element array consisting of:

• A value returned by the block.

• An array (“chunk”) containing the element for which that value was returned, and all following elements for which the block returned the same value:

So that:

• Each block return value that is different from its predecessor begins a new chunk.

• Each block return value that is the same as its predecessor continues the same chunk.

Example:

e = (0..10).chunk {|i| (i / 3).floor } # => #<Enumerator: ...>
# The enumerator elements.
e.next # => [0, [0, 1, 2]]
e.next # => [1, [3, 4, 5]]
e.next # => [2, [6, 7, 8]]
e.next # => [3, [9, 10]]

Method chunk is especially useful for an enumerable that is already sorted. This example counts words for each initial letter in a large array of words:

# Get sorted words from a web page.
url = 'https://raw.githubusercontent.com/eneko/data-repository/master/data/words.txt'
words = URI::open(url).readlines
# Make chunks, one for each letter.
e = words.chunk {|word| word.upcase[0] } # => #<Enumerator: ...>
# Display 'A' through 'F'.
e.each {|c, words| p [c, words.length]; break if c == 'F' }

Output:

["A", 17096]
["B", 11070]
["C", 19901]
["D", 10896]
["E", 8736]
["F", 6860]

You can use the special symbol :_alone to force an element into its own separate chuck:

a = [0, 0, 1, 1]
e = a.chunk{|i| i.even? ? :_alone : true }
e.to_a # => [[:_alone, [0]], [:_alone, [0]], [true, [1, 1]]]

For example, you can put each line that contains a URL into its own chunk:

pattern = /http/
open(filename) { |f|
  f.chunk { |line| line =~ pattern ? :_alone : true }.each { |key, lines|
    pp lines
  }
}

You can use the special symbol :_separator or nil to force an element to be ignored (not included in any chunk):

a = [0, 0, -1, 1, 1]
e = a.chunk{|i| i < 0 ? :_separator : true }
e.to_a # => [[true, [0, 0]], [true, [1, 1]]]

Note that the separator does end the chunk:

a = [0, 0, -1, 1, -1, 1]
e = a.chunk{|i| i < 0 ? :_separator : true }
e.to_a # => [[true, [0, 0]], [true, [1]], [true, [1]]]

For example, the sequence of hyphens in svn log can be eliminated as follows:

sep = "-"*72 + "\n"
IO.popen("svn log README") { |f|
  f.chunk { |line|
    line != sep || nil
  }.each { |_, lines|
    pp lines
  }
}
#=> ["r20018 | knu | 2008-10-29 13:20:42 +0900 (Wed, 29 Oct 2008) | 2 lines\n",
#    "\n",
#    "* README, README.ja: Update the portability section.\n",
#    "\n"]
#   ["r16725 | knu | 2008-05-31 23:34:23 +0900 (Sat, 31 May 2008) | 2 lines\n",
#    "\n",
#    "* README, README.ja: Add a note about default C flags.\n",
#    "\n"]
#   ...

Paragraphs separated by empty lines can be parsed as follows:

File.foreach("README").chunk { |line|
  /\A\s*\z/ !~ line || nil
}.each { |_, lines|
  pp lines
}

Creates an enumerator for each chunked elements. The beginnings of chunks are defined by the block.

This method splits each chunk using adjacent elements, elt_before and elt_after, in the receiver enumerator. This method split chunks between elt_before and elt_after where the block returns false.

The block is called the length of the receiver enumerator minus one.

The result enumerator yields the chunked elements as an array. So each method can be called as follows:

enum.chunk_while { |elt_before, elt_after| bool }.each { |ary| ... }

Other methods of the Enumerator class and Enumerable module, such as to_a, map, etc., are also usable.

For example, one-by-one increasing subsequence can be chunked as follows:

a = [1,2,4,9,10,11,12,15,16,19,20,21]
b = a.chunk_while {|i, j| i+1 == j }
p b.to_a #=> [[1, 2], [4], [9, 10, 11, 12], [15, 16], [19, 20, 21]]
c = b.map {|a| a.length < 3 ? a : "#{a.first}-#{a.last}" }
p c #=> [[1, 2], [4], "9-12", [15, 16], "19-21"]
d = c.join(",")
p d #=> "1,2,4,9-12,15,16,19-21"

Increasing (non-decreasing) subsequence can be chunked as follows:

a = [0, 9, 2, 2, 3, 2, 7, 5, 9, 5]
p a.chunk_while {|i, j| i <= j }.to_a
#=> [[0, 9], [2, 2, 3], [2, 7], [5, 9], [5]]

Adjacent evens and odds can be chunked as follows: (Enumerable#chunk is another way to do it.)

a = [7, 5, 9, 2, 0, 7, 9, 4, 2, 0]
p a.chunk_while {|i, j| i.even? == j.even? }.to_a
#=> [[7, 5, 9], [2, 0], [7, 9], [4, 2, 0]]

Enumerable#slice_when does the same, except splitting when the block returns true instead of false.

Returns an array of objects returned by the block.

With a block given, calls the block with successive elements; returns an array of the objects returned by the block:

(0..4).map {|i| i*i }                               # => [0, 1, 4, 9, 16]
{foo: 0, bar: 1, baz: 2}.map {|key, value| value*2} # => [0, 2, 4]

With no block given, returns an Enumerator.

Returns an array of all non-nil elements:

a = [nil, 0, nil, 'a', false, nil, false, nil, 'a', nil, 0, nil]
a.compact # => [0, "a", false, false, "a", 0]

Returns the count of elements, based on an argument or block criterion, if given.

With no argument and no block given, returns the number of elements:

[0, 1, 2].count                # => 3
{foo: 0, bar: 1, baz: 2}.count # => 3

With argument object given, returns the number of elements that are == to object:

[0, 1, 2, 1].count(1)           # => 2

With a block given, calls the block with each element and returns the number of elements for which the block returns a truthy value:

[0, 1, 2, 3].count {|element| element < 2}              # => 2
{foo: 0, bar: 1, baz: 2}.count {|key, value| value < 2} # => 2

When called with positive integer argument n and a block, calls the block with each element, then does so again, until it has done so n times; returns nil:

a = []
(1..4).cycle(3) {|element| a.push(element) } # => nil
a # => [1, 2, 3, 4, 1, 2, 3, 4, 1, 2, 3, 4]
a = []
('a'..'d').cycle(2) {|element| a.push(element) }
a # => ["a", "b", "c", "d", "a", "b", "c", "d"]
a = []
{foo: 0, bar: 1, baz: 2}.cycle(2) {|element| a.push(element) }
a # => [[:foo, 0], [:bar, 1], [:baz, 2], [:foo, 0], [:bar, 1], [:baz, 2]]

If count is zero or negative, does not call the block.

When called with a block and n is nil, cycles forever.

When no block is given, returns an Enumerator.

For positive integer n, returns an array containing all but the first n elements:

r = (1..4)
r.drop(3)  # => [4]
r.drop(2)  # => [3, 4]
r.drop(1)  # => [2, 3, 4]
r.drop(0)  # => [1, 2, 3, 4]
r.drop(50) # => []

h = {foo: 0, bar: 1, baz: 2, bat: 3}
h.drop(2) # => [[:baz, 2], [:bat, 3]]

Calls the block with successive elements as long as the block returns a truthy value; returns an array of all elements after that point:

(1..4).drop_while{|i| i < 3 } # => [3, 4]
h = {foo: 0, bar: 1, baz: 2}
a = h.drop_while{|element| key, value = *element; value < 2 }
a # => [[:baz, 2]]

With no block given, returns an Enumerator.

Calls the block with each successive overlapped n-tuple of elements; returns self:

a = []
(1..5).each_cons(3) {|element| a.push(element) }
a # => [[1, 2, 3], [2, 3, 4], [3, 4, 5]]

a = []
h = {foo: 0,  bar: 1, baz: 2, bam: 3}
h.each_cons(2) {|element| a.push(element) }
a # => [[[:foo, 0], [:bar, 1]], [[:bar, 1], [:baz, 2]], [[:baz, 2], [:bam, 3]]]

With no block given, returns an Enumerator.

Calls the given block with each element, converting multiple values from yield to an array; returns self:

a = []
(1..4).each_entry {|element| a.push(element) } # => 1..4
a # => [1, 2, 3, 4]

a = []
h = {foo: 0, bar: 1, baz:2}
h.each_entry {|element| a.push(element) }
# => {:foo=>0, :bar=>1, :baz=>2}
a # => [[:foo, 0], [:bar, 1], [:baz, 2]]

class Foo
  include Enumerable
  def each
    yield 1
    yield 1, 2
    yield
  end
end
Foo.new.each_entry {|yielded| p yielded }

Output:

1
[1, 2]
nil

With no block given, returns an Enumerator.

Calls the block with each successive disjoint n-tuple of elements; returns self:

a = []
(1..10).each_slice(3) {|tuple| a.push(tuple) }
a # => [[1, 2, 3], [4, 5, 6], [7, 8, 9], [10]]

a = []
h = {foo: 0, bar: 1, baz: 2, bat: 3, bam: 4}
h.each_slice(2) {|tuple| a.push(tuple) }
a # => [[[:foo, 0], [:bar, 1]], [[:baz, 2], [:bat, 3]], [[:bam, 4]]]

With no block given, returns an Enumerator.

With a block given, calls the block with each element and its index; returns self:

h = {}
(1..4).each_with_index {|element, i| h[element] = i } # => 1..4
h # => {1=>0, 2=>1, 3=>2, 4=>3}

h = {}
%w[a b c d].each_with_index {|element, i| h[element] = i }
# => ["a", "b", "c", "d"]
h # => {"a"=>0, "b"=>1, "c"=>2, "d"=>3}

a = []
h = {foo: 0, bar: 1, baz: 2}
h.each_with_index {|element, i| a.push([i, element]) }
# => {:foo=>0, :bar=>1, :baz=>2}
a # => [[0, [:foo, 0]], [1, [:bar, 1]], [2, [:baz, 2]]]

With no block given, returns an Enumerator.

Calls the block once for each element, passing both the element and the given object:

(1..4).each_with_object([]) {|i, a| a.push(i**2) }
# => [1, 4, 9, 16]

{foo: 0, bar: 1, baz: 2}.each_with_object({}) {|(k, v), h| h[v] = k }
# => {0=>:foo, 1=>:bar, 2=>:baz}

With no block given, returns an Enumerator.

Returns an array containing truthy elements returned by the block.

With a block given, calls the block with successive elements; returns an array containing each truthy value returned by the block:

(0..9).filter_map {|i| i * 2 if i.even? }                              # => [0, 4, 8, 12, 16]
{foo: 0, bar: 1, baz: 2}.filter_map {|key, value| key if value.even? } # => [:foo, :baz]

When no block given, returns an Enumerator.

Returns the first element for which the block returns a truthy value.

With a block given, calls the block with successive elements of the collection; returns the first element for which the block returns a truthy value:

(0..9).find {|element| element > 2}                # => 3

If no such element is found, calls if_none_proc and returns its return value.

(0..9).find(proc {false}) {|element| element > 12} # => false
{foo: 0, bar: 1, baz: 2}.find {|key, value| key.start_with?('b') }            # => [:bar, 1]
{foo: 0, bar: 1, baz: 2}.find(proc {[]}) {|key, value| key.start_with?('c') } # => []

With no block given, returns an Enumerator.

Returns an array containing elements selected by the block.

With a block given, calls the block with successive elements; returns an array of those elements for which the block returns a truthy value:

(0..9).select {|element| element % 3 == 0 } # => [0, 3, 6, 9]
a = {foo: 0, bar: 1, baz: 2}.select {|key, value| key.start_with?('b') }
a # => {:bar=>1, :baz=>2}

With no block given, returns an Enumerator.

Related: reject.

Returns the index of the first element that meets a specified criterion, or nil if no such element is found.

With argument object given, returns the index of the first element that is == object:

['a', 'b', 'c', 'b'].find_index('b') # => 1

With a block given, calls the block with successive elements; returns the first element for which the block returns a truthy value:

['a', 'b', 'c', 'b'].find_index {|element| element.start_with?('b') } # => 1
{foo: 0, bar: 1, baz: 2}.find_index {|key, value| value > 1 }         # => 2

With no argument and no block given, returns an Enumerator.

Returns the first element or elements.

With no argument, returns the first element, or nil if there is none:

(1..4).first                   # => 1
%w[a b c].first                # => "a"
{foo: 1, bar: 1, baz: 2}.first # => [:foo, 1]
[].first                       # => nil

With integer argument n, returns an array containing the first n elements that exist:

(1..4).first(2)                   # => [1, 2]
%w[a b c d].first(3)              # => ["a", "b", "c"]
%w[a b c d].first(50)             # => ["a", "b", "c", "d"]
{foo: 1, bar: 1, baz: 2}.first(2) # => [[:foo, 1], [:bar, 1]]
[].first(2)                       # => []

Returns an array of flattened objects returned by the block.

With a block given, calls the block with successive elements; returns a flattened array of objects returned by the block:

[0, 1, 2, 3].flat_map {|element| -element }                    # => [0, -1, -2, -3]
[0, 1, 2, 3].flat_map {|element| [element, -element] }         # => [0, 0, 1, -1, 2, -2, 3, -3]
[[0, 1], [2, 3]].flat_map {|e| e + [100] }                     # => [0, 1, 100, 2, 3, 100]
{foo: 0, bar: 1, baz: 2}.flat_map {|key, value| [key, value] } # => [:foo, 0, :bar, 1, :baz, 2]

With no block given, returns an Enumerator.

Alias: collect_concat.

Returns an array of objects based elements of self that match the given pattern.

With no block given, returns an array containing each element for which pattern === element is true:

a = ['foo', 'bar', 'car', 'moo']
a.grep(/ar/)                   # => ["bar", "car"]
(1..10).grep(3..8)             # => [3, 4, 5, 6, 7, 8]
['a', 'b', 0, 1].grep(Integer) # => [0, 1]

With a block given, calls the block with each matching element and returns an array containing each object returned by the block:

a = ['foo', 'bar', 'car', 'moo']
a.grep(/ar/) {|element| element.upcase } # => ["BAR", "CAR"]

Related: grep_v.

Returns an array of objects based on elements of self that don’t match the given pattern.

With no block given, returns an array containing each element for which pattern === element is false:

a = ['foo', 'bar', 'car', 'moo']
a.grep_v(/ar/)                   # => ["foo", "moo"]
(1..10).grep_v(3..8)             # => [1, 2, 9, 10]
['a', 'b', 0, 1].grep_v(Integer) # => ["a", "b"]

With a block given, calls the block with each non-matching element and returns an array containing each object returned by the block:

a = ['foo', 'bar', 'car', 'moo']
a.grep_v(/ar/) {|element| element.upcase } # => ["FOO", "MOO"]

Related: grep.

With a block given returns a hash:

• Each key is a return value from the block.

• Each value is an array of those elements for which the block returned that key.

Examples:

g = (1..6).group_by {|i| i%3 }
g # => {1=>[1, 4], 2=>[2, 5], 0=>[3, 6]}
h = {foo: 0, bar: 1, baz: 0, bat: 1}
g = h.group_by {|key, value| value }
g # => {0=>[[:foo, 0], [:baz, 0]], 1=>[[:bar, 1], [:bat, 1]]}

With no block given, returns an Enumerator.

Returns an object formed from operands via either:

• A method named by symbol.

• A block to which each operand is passed.

With method-name argument symbol, combines operands using the method:

# Sum, without initial_operand.
(1..4).inject(:+)     # => 10
# Sum, with initial_operand.
(1..4).inject(10, :+) # => 20

With a block, passes each operand to the block:

# Sum of squares, without initial_operand.
(1..4).inject {|sum, n| sum + n*n }    # => 30
# Sum of squares, with initial_operand.
(1..4).inject(2) {|sum, n| sum + n*n } # => 32

Operands

If argument initial_operand is not given, the operands for inject are simply the elements of self. Example calls and their operands:

• (1..4).inject(:+)

  [1, 2, 3, 4].

• (1...4).inject(:+)

  [1, 2, 3].

• ('a'..'d').inject(:+)

  ['a', 'b', 'c', 'd'].

• ('a'...'d').inject(:+)

  ['a', 'b', 'c'].

Examples with first operand (which is self.first) of various types:

# Integer.
(1..4).inject(:+)                # => 10
# Float.
[1.0, 2, 3, 4].inject(:+)        # => 10.0
# Character.
('a'..'d').inject(:+)            # => "abcd"
# Complex.
[Complex(1, 2), 3, 4].inject(:+) # => (8+2i)

If argument initial_operand is given, the operands for inject are that value plus the elements of self. Example calls their operands:

• (1..4).inject(10, :+)

  [10, 1, 2, 3, 4].

• (1...4).inject(10, :+)

  [10, 1, 2, 3].

• ('a'..'d').inject('e', :+)

  ['e', 'a', 'b', 'c', 'd'].

• ('a'...'d').inject('e', :+)

  ['e', 'a', 'b', 'c'].

Examples with initial_operand of various types:

# Integer.
(1..4).inject(2, :+)               # => 12
# Float.
(1..4).inject(2.0, :+)             # => 12.0
# String.
('a'..'d').inject('foo', :+)       # => "fooabcd"
# Array.
%w[a b c].inject(['x'], :push)     # => ["x", "a", "b", "c"]
# Complex.
(1..4).inject(Complex(2, 2), :+)   # => (12+2i)

Combination by Given Method

If the method-name argument symbol is given, the operands are combined by that method:

• The first and second operands are combined.

• That result is combined with the third operand.

• That result is combined with the fourth operand.

• And so on.

The return value from inject is the result of the last combination.

This call to inject computes the sum of the operands:

(1..4).inject(:+) # => 10

Examples with various methods:

# Integer addition.
(1..4).inject(:+)                # => 10
# Integer multiplication.
(1..4).inject(:*)                # => 24
# Character range concatenation.
('a'..'d').inject('', :+)        # => "abcd"
# String array concatenation.
%w[foo bar baz].inject('', :+)   # => "foobarbaz"
# Hash update.
h = [{foo: 0, bar: 1}, {baz: 2}, {bat: 3}].inject(:update)
h # => {:foo=>0, :bar=>1, :baz=>2, :bat=>3}
# Hash conversion to nested arrays.
h = {foo: 0, bar: 1}.inject([], :push)
h # => [[:foo, 0], [:bar, 1]]

Combination by Given Block

If a block is given, the operands are passed to the block:

• The first call passes the first and second operands.

• The second call passes the result of the first call, along with the third operand.

• The third call passes the result of the second call, along with the fourth operand.

• And so on.

The return value from inject is the return value from the last block call.

This call to inject gives a block that writes the memo and element, and also sums the elements:

(1..4).inject do |memo, element|
  p "Memo: #{memo}; element: #{element}"
  memo + element
end # => 10

Output:

"Memo: 1; element: 2"
"Memo: 3; element: 3"
"Memo: 6; element: 4"

Returns an Enumerator::Lazy, which redefines most Enumerable methods to postpone enumeration and enumerate values only on an as-needed basis.

Example

The following program finds pythagorean triples:

def pythagorean_triples
  (1..Float::INFINITY).lazy.flat_map {|z|
    (1..z).flat_map {|x|
      (x..z).select {|y|
        x**2 + y**2 == z**2
      }.map {|y|
        [x, y, z]
      }
    }
  }
end
# show first ten pythagorean triples
p pythagorean_triples.take(10).force # take is lazy, so force is needed
p pythagorean_triples.first(10)      # first is eager
# show pythagorean triples less than 100
p pythagorean_triples.take_while { |*, z| z < 100 }.force

Returns the element with the maximum element according to a given criterion. The ordering of equal elements is indeterminate and may be unstable.

With no argument and no block, returns the maximum element, using the elements’ own method <=> for comparison:

(1..4).max                   # => 4
(-4..-1).max                 # => -1
%w[d c b a].max              # => "d"
{foo: 0, bar: 1, baz: 2}.max # => [:foo, 0]
[].max                       # => nil

With positive integer argument n given, and no block, returns an array containing the first n maximum elements that exist:

(1..4).max(2)                   # => [4, 3]
(-4..-1).max(2)                # => [-1, -2]
%w[d c b a].max(2)              # => ["d", "c"]
{foo: 0, bar: 1, baz: 2}.max(2) # => [[:foo, 0], [:baz, 2]]
[].max(2)                       # => []

With a block given, the block determines the maximum elements. The block is called with two elements a and b, and must return:

• A negative integer if a < b.

• Zero if a == b.

• A positive integer if a > b.

With a block given and no argument, returns the maximum element as determined by the block:

%w[xxx x xxxx xx].max {|a, b| a.size <=> b.size } # => "xxxx"
h = {foo: 0, bar: 1, baz: 2}
h.max {|pair1, pair2| pair1[1] <=> pair2[1] }     # => [:baz, 2]
[].max {|a, b| a <=> b }                          # => nil

With a block given and positive integer argument n given, returns an array containing the first n maximum elements that exist, as determined by the block.

%w[xxx x xxxx xx].max(2) {|a, b| a.size <=> b.size } # => ["xxxx", "xxx"]
h = {foo: 0, bar: 1, baz: 2}
h.max(2) {|pair1, pair2| pair1[1] <=> pair2[1] }
# => [[:baz, 2], [:bar, 1]]
[].max(2) {|a, b| a <=> b }                          # => []

Related: min, minmax, max_by.

Returns the elements for which the block returns the maximum values.

With a block given and no argument, returns the element for which the block returns the maximum value:

(1..4).max_by {|element| -element }                    # => 1
%w[a b c d].max_by {|element| -element.ord }           # => "a"
{foo: 0, bar: 1, baz: 2}.max_by {|key, value| -value } # => [:foo, 0]
[].max_by {|element| -element }                        # => nil

With a block given and positive integer argument n given, returns an array containing the n elements for which the block returns maximum values:

(1..4).max_by(2) {|element| -element }
# => [1, 2]
%w[a b c d].max_by(2) {|element| -element.ord }
# => ["a", "b"]
{foo: 0, bar: 1, baz: 2}.max_by(2) {|key, value| -value }
# => [[:foo, 0], [:bar, 1]]
[].max_by(2) {|element| -element }
# => []

Returns an Enumerator if no block is given.

Related: max, minmax, min_by.

Returns whether for any element object == element:

(1..4).include?(2)                       # => true
(1..4).include?(5)                       # => false
(1..4).include?('2')                     # => false
%w[a b c d].include?('b')                # => true
%w[a b c d].include?('2')                # => false
{foo: 0, bar: 1, baz: 2}.include?(:foo)  # => true
{foo: 0, bar: 1, baz: 2}.include?('foo') # => false
{foo: 0, bar: 1, baz: 2}.include?(0)     # => false

Returns the element with the minimum element according to a given criterion. The ordering of equal elements is indeterminate and may be unstable.

With no argument and no block, returns the minimum element, using the elements’ own method <=> for comparison:

(1..4).min                   # => 1
(-4..-1).min                 # => -4
%w[d c b a].min              # => "a"
{foo: 0, bar: 1, baz: 2}.min # => [:bar, 1]
[].min                       # => nil

With positive integer argument n given, and no block, returns an array containing the first n minimum elements that exist:

(1..4).min(2)                   # => [1, 2]
(-4..-1).min(2)                 # => [-4, -3]
%w[d c b a].min(2)              # => ["a", "b"]
{foo: 0, bar: 1, baz: 2}.min(2) # => [[:bar, 1], [:baz, 2]]
[].min(2)                       # => []

With a block given, the block determines the minimum elements. The block is called with two elements a and b, and must return:

• A negative integer if a < b.

• Zero if a == b.

• A positive integer if a > b.

With a block given and no argument, returns the minimum element as determined by the block:

%w[xxx x xxxx xx].min {|a, b| a.size <=> b.size } # => "x"
h = {foo: 0, bar: 1, baz: 2}
h.min {|pair1, pair2| pair1[1] <=> pair2[1] } # => [:foo, 0]
[].min {|a, b| a <=> b }                          # => nil

With a block given and positive integer argument n given, returns an array containing the first n minimum elements that exist, as determined by the block.

%w[xxx x xxxx xx].min(2) {|a, b| a.size <=> b.size } # => ["x", "xx"]
h = {foo: 0, bar: 1, baz: 2}
h.min(2) {|pair1, pair2| pair1[1] <=> pair2[1] }
# => [[:foo, 0], [:bar, 1]]
[].min(2) {|a, b| a <=> b }                          # => []

Related: min_by, minmax, max.

Returns the elements for which the block returns the minimum values.

With a block given and no argument, returns the element for which the block returns the minimum value:

(1..4).min_by {|element| -element }                    # => 4
%w[a b c d].min_by {|element| -element.ord }           # => "d"
{foo: 0, bar: 1, baz: 2}.min_by {|key, value| -value } # => [:baz, 2]
[].min_by {|element| -element }                        # => nil

With a block given and positive integer argument n given, returns an array containing the n elements for which the block returns minimum values:

(1..4).min_by(2) {|element| -element }
# => [4, 3]
%w[a b c d].min_by(2) {|element| -element.ord }
# => ["d", "c"]
{foo: 0, bar: 1, baz: 2}.min_by(2) {|key, value| -value }
# => [[:baz, 2], [:bar, 1]]
[].min_by(2) {|element| -element }
# => []

Returns an Enumerator if no block is given.

Related: min, minmax, max_by.

Returns a 2-element array containing the minimum and maximum elements according to a given criterion. The ordering of equal elements is indeterminate and may be unstable.

With no argument and no block, returns the minimum and maximum elements, using the elements’ own method <=> for comparison:

(1..4).minmax                   # => [1, 4]
(-4..-1).minmax                 # => [-4, -1]
%w[d c b a].minmax              # => ["a", "d"]
{foo: 0, bar: 1, baz: 2}.minmax # => [[:bar, 1], [:foo, 0]]
[].minmax                       # => [nil, nil]

With a block given, returns the minimum and maximum elements as determined by the block:

%w[xxx x xxxx xx].minmax {|a, b| a.size <=> b.size } # => ["x", "xxxx"]
h = {foo: 0, bar: 1, baz: 2}
h.minmax {|pair1, pair2| pair1[1] <=> pair2[1] }
# => [[:foo, 0], [:baz, 2]]
[].minmax {|a, b| a <=> b }                          # => [nil, nil]

Related: min, max, minmax_by.

Returns a 2-element array containing the elements for which the block returns minimum and maximum values:

(1..4).minmax_by {|element| -element }
# => [4, 1]
%w[a b c d].minmax_by {|element| -element.ord }
# => ["d", "a"]
{foo: 0, bar: 1, baz: 2}.minmax_by {|key, value| -value }
# => [[:baz, 2], [:foo, 0]]
[].minmax_by {|element| -element }
# => [nil, nil]

Returns an Enumerator if no block is given.

Related: max_by, minmax, min_by.

Returns whether no element meets a given criterion.

With no argument and no block, returns whether no element is truthy:

(1..4).none?           # => false
[nil, false].none?     # => true
{foo: 0}.none?         # => false
{foo: 0, bar: 1}.none? # => false
[].none?               # => true

With argument pattern and no block, returns whether for no element element, pattern === element:

[nil, false, 1.1].none?(Integer)      # => true
%w[bar baz bat bam].none?(/m/)        # => false
%w[bar baz bat bam].none?(/foo/)      # => true
%w[bar baz bat bam].none?('ba')       # => true
{foo: 0, bar: 1, baz: 2}.none?(Hash)  # => true
{foo: 0}.none?(Array)                 # => false
[].none?(Integer)                     # => true

With a block given, returns whether the block returns a truthy value for no element:

(1..4).none? {|element| element < 1 }                     # => true
(1..4).none? {|element| element < 2 }                     # => false
{foo: 0, bar: 1, baz: 2}.none? {|key, value| value < 0 }  # => true
{foo: 0, bar: 1, baz: 2}.none? {|key, value| value < 1 } # => false

Related: one?, all?, any?.

Returns whether exactly one element meets a given criterion.

With no argument and no block, returns whether exactly one element is truthy:

(1..1).one?           # => true
[1, nil, false].one?  # => true
(1..4).one?           # => false
{foo: 0}.one?         # => true
{foo: 0, bar: 1}.one? # => false
[].one?               # => false

With argument pattern and no block, returns whether for exactly one element element, pattern === element:

[nil, false, 0].one?(Integer)        # => true
[nil, false, 0].one?(Numeric)        # => true
[nil, false, 0].one?(Float)          # => false
%w[bar baz bat bam].one?(/m/)        # => true
%w[bar baz bat bam].one?(/foo/)      # => false
%w[bar baz bat bam].one?('ba')       # => false
{foo: 0, bar: 1, baz: 2}.one?(Array) # => false
{foo: 0}.one?(Array)                 # => true
[].one?(Integer)                     # => false

With a block given, returns whether the block returns a truthy value for exactly one element:

(1..4).one? {|element| element < 2 }                     # => true
(1..4).one? {|element| element < 1 }                     # => false
{foo: 0, bar: 1, baz: 2}.one? {|key, value| value < 1 }  # => true
{foo: 0, bar: 1, baz: 2}.one? {|key, value| value < 2 } # => false

Related: none?, all?, any?.

With a block given, returns an array of two arrays:

• The first having those elements for which the block returns a truthy value.

• The other having all other elements.

Examples:

p = (1..4).partition {|i| i.even? }
p # => [[2, 4], [1, 3]]
p = ('a'..'d').partition {|c| c < 'c' }
p # => [["a", "b"], ["c", "d"]]
h = {foo: 0, bar: 1, baz: 2, bat: 3}
p = h.partition {|key, value| key.start_with?('b') }
p # => [[[:bar, 1], [:baz, 2], [:bat, 3]], [[:foo, 0]]]
p = h.partition {|key, value| value < 2 }
p # => [[[:foo, 0], [:bar, 1]], [[:baz, 2], [:bat, 3]]]