Returns a value with the same type as an element of x, even if x is not an Enumerable.

Used by splat expansion inside array literals. For example, this code

[1, *{2, 3.5}, 4]

will end up calling typeof(1, ::Enumerable.element_type({2, 3.5}), 4).

NOTE there should never be a need to call this method outside the standard library.

Returns an array containing initial and its prefix sums with the elements in this collection.

Expects U to respond to the #+ method.

[1, 2, 3, 4, 5].accumulate(6) # => [6, 7, 9, 12, 16, 21]

Returns an array of the prefix sums of the elements in this collection. The first element of the returned array is same as the first element of self.

Expects all element types to respond to the #+ method.

[1, 2, 3, 4, 5, 6].accumulate # => [1, 3, 6, 10, 15, 21]

Returns an array containing initial and the successive values of applying a binary operation, specified by the given block, to this collection's elements.

Similar to #accumulate(&block : T, T -> T), except the initial value is provided by an argument and needs not have the same type as the elements in the collection. This initial value is always present in the returned array.

[1, 3, 5, 7].accumulate(9) { |x, y| x * y } # => [9, 9, 27, 135, 945]

Returns an array containing the successive values of applying a binary operation, specified by the given block, to this collection's elements.

For each element in the collection the block is passed an accumulator value and the element. The result becomes the new value for the accumulator and is also appended to the returned array. The initial value for the accumulator is the first element in the collection.

[2, 3, 4, 5].accumulate { |x, y| x * y } # => [2, 6, 24, 120]

Returns true if the passed block returns a value other than false or nil for all elements of the collection.

["ant", "bear", "cat"].all? { |word| word.size >= 3 } # => true
["ant", "bear", "cat"].all? { |word| word.size >= 4 } # => false

Returns true if pattern === element for all elements in this enumerable.

[2, 3, 4].all?(1..5)        # => true
[2, 3, 4].all?(Int32)       # => true
[2, "a", 3].all?(String)    # => false
%w[foo bar baz].all?(/o|a/) # => true

Returns true if none of the elements of the collection is false or nil.

[nil, true, 99].all? # => false
[15].all?            # => true

Returns true if the passed block returns a value other than false or nil for at least one element of the collection.

["ant", "bear", "cat"].any? { |word| word.size >= 4 } # => true
["ant", "bear", "cat"].any? { |word| word.size > 4 }  # => false

Returns true if pattern === element for at least one element in this enumerable.

[2, 3, 4].any?(1..3)      # => true
[2, 3, 4].any?(5..10)     # => false
[2, "a", 3].any?(String)  # => true
%w[foo bar baz].any?(/a/) # => true

Returns true if at least one of the collection members is not false or nil.

[nil, true, 99].any? # => true
[nil, false].any?    # => false

Enumerates over the items, chunking them together based on the return value of the block.

Consecutive elements which return the same block value are chunked together.

For example, consecutive even numbers and odd numbers can be chunked as follows.

ary = [3, 1, 4, 1, 5, 9, 2, 6, 5, 3, 5].chunks { |n| n.even? }
ary # => [{false, [3, 1]}, {true, [4]}, {false, [1, 5, 9]}, {true, [2, 6]}, {false, [5, 3, 5]}]

The following key values have special meaning:

• Enumerable::Chunk::Drop specifies that the elements should be dropped
• Enumerable::Chunk::Alone specifies that the element should be chunked by itself

See also: Iterator#chunk.

Returns an Array with the results of running the block against each element of the collection, removing nil values.

["Alice", "Bob"].map { |name| name.match(/^A./) }         # => [Regex::MatchData("Al"), nil]
["Alice", "Bob"].compact_map { |name| name.match(/^A./) } # => [Regex::MatchData("Al")]

Returns the number of elements in the collection for which the passed block returns true.

[1, 2, 3, 4].count { |i| i % 2 == 0 } # => 2

Returns the number of times that the passed item is present in the collection.

[1, 2, 3, 4].count(3) # => 1

Calls the given block for each element in this enumerable n times.

Calls the given block for each element in this enumerable forever.

Must yield this collection's elements to the block.

Iterates over the collection yielding chunks of size count, but advancing one by one.

[1, 2, 3, 4, 5].each_cons(2) do |cons|
  puts cons
end

Prints:

[1, 2]
[2, 3]
[3, 4]
[4, 5]

By default, a new array is created and yielded for each consecutive slice of elements.

• If reuse is given, the array can be reused
• If reuse is true, the method will create a new array and reuse it.
• If reuse is an instance of Array, Deque or a similar collection type (implementing #<<, #shift and #size) it will be used.
• If reuse is falsey, the array will not be reused.

This can be used to prevent many memory allocations when each slice of interest is to be used in a read-only fashion.

Chunks of two items can be iterated using #each_cons_pair, an optimized implementation for the special case of size == 2 which avoids heap allocations.

Iterates over the collection yielding pairs of adjacent items, but advancing one by one.

[1, 2, 3, 4, 5].each_cons_pair do |a, b|
  puts "#{a}, #{b}"
end

Prints:

1, 2
2, 3
3, 4
4, 5

Chunks of more than two items can be iterated using #each_cons. This method is just an optimized implementation for the special case of size == 2 to avoid heap allocations.

Iterates over the collection in slices of size count, and runs the block for each of those.

[1, 2, 3, 4, 5].each_slice(2) do |slice|
  puts slice
end

Prints:

[1, 2]
[3, 4]
[5]

Note that the last one can be smaller.

By default, a new array is created and yielded for each slice.

• If reuse is given, the array can be reused
• If reuse is an Array, this array will be reused
• If reuse is truthy, the method will create a new array and reuse it.

This can be used to prevent many memory allocations when each slice of interest is to be used in a read-only fashion.

Iterates over the collection, yielding both the elements and their index.

["Alice", "Bob"].each_with_index do |user, i|
  puts "User ##{i}: #{user}"
end

Prints:

User # 0: Alice
User # 1: Bob

Accepts an optional offset parameter, which tells it to start counting from there. So, a more human friendly version of the previous snippet would be:

["Alice", "Bob"].each_with_index(1) do |user, i|
  puts "User ##{i}: #{user}"
end

Which would print:

User # 1: Alice
User # 2: Bob

Iterates over the collection, passing each element and the initial object obj. Returns that object.

hash = ["Alice", "Bob"].each_with_object({} of String => Int32) do |user, sizes|
  sizes[user] = user.size
end
hash # => {"Alice" => 5, "Bob" => 3}

Returns true if self is empty, false otherwise.

([] of Int32).empty? # => true
([1]).empty?         # => false

Returns the first element in the collection for which the passed block is true.

Accepts an optional parameter if_none, to set what gets returned if no element is found (defaults to nil).

[1, 2, 3, 4].find { |i| i > 2 }     # => 3
[1, 2, 3, 4].find { |i| i > 8 }     # => nil
[1, 2, 3, 4].find(-1) { |i| i > 8 } # => -1

Returns the first element in the collection, If the collection is empty, calls the block and returns its value.

([1, 2, 3]).first { 4 }   # => 1
([] of Int32).first { 4 } # => 4

Returns an Array with the first count elements in the collection.

If count is bigger than the number of elements in the collection, returns as many as possible. This include the case of calling it over an empty collection, in which case it returns an empty array.

Returns the first element in the collection. Raises Enumerable::EmptyError if the collection is empty.

([1, 2, 3]).first   # => 1
([] of Int32).first # raises Enumerable::EmptyError

Returns the first element in the collection. When the collection is empty, returns nil.

([1, 2, 3]).first?   # => 1
([] of Int32).first? # => nil

Returns a new array with the concatenated results of running the block once for every element in the collection. Only Array and Iterator results are concatenated; every other value is directly appended to the new array.

array = ["Alice", "Bob"].flat_map do |user|
  user.chars
end
array # => ['A', 'l', 'i', 'c', 'e', 'B', 'o', 'b']

Returns a Hash whose keys are each different value that the passed block returned when run for each element in the collection, and which values are an Array of the elements for which the block returned that value.

["Alice", "Bob", "Ary"].group_by { |name| name.size } # => {5 => ["Alice"], 3 => ["Bob", "Ary"]}

Returns an Array with chunks in the given size, eventually filled up with given value or nil.

[1, 2, 3].in_groups_of(2, 0) # => [[1, 2], [3, 0]]
[1, 2, 3].in_groups_of(2)    # => [[1, 2], [3, nil]]

Yields a block with the chunks in the given size.

[1, 2, 4].in_groups_of(2, 0) { |e| p e.sum }
# => 3
# => 4

By default, a new array is created and yielded for each group.

• If reuse is given, the array can be reused
• If reuse is an Array, this array will be reused
• If reuse is truthy, the method will create a new array and reuse it.

This can be used to prevent many memory allocations when each slice of interest is to be used in a read-only fashion.

Returns true if the collection contains obj, false otherwise.

[1, 2, 3].includes?(2) # => true
[1, 2, 3].includes?(5) # => false

Returns the index of the first element for which the passed block returns true.

["Alice", "Bob"].index { |name| name.size < 4 } # => 1 (Bob's index)

Returns nil if the block didn't return true for any element.

Returns the index of the object obj in the collection.

["Alice", "Bob"].index("Alice") # => 0

Returns nil if obj is not in the collection.

Converts an Enumerable to a Hash by using the value returned by the block as the hash key. Be aware, if two elements return the same value as a key one will override the other. If you want to keep all values, then you should probably use #group_by instead.

["Anna", "Ary", "Alice"].index_by { |e| e.size }
# => {4 => "Anna", 3 => "Ary", 5 => "Alice"}
["Anna", "Ary", "Alice", "Bob"].index_by { |e| e.size }
# => {4 => "Anna", 3 => "Bob", 5 => "Alice"}

Prints to io all the elements in the collection, separated by separator.

[1, 2, 3, 4, 5].join(STDOUT, ", ")

Prints:

1, 2, 3, 4, 5

Prints to io all the elements in the collection, separated by separator.

[1, 2, 3, 4, 5].join(STDOUT, ", ")

Prints:

1, 2, 3, 4, 5

DEPRECATED Use #join(io : IO, separator = "") instead

Returns a String created by concatenating the elements in the collection, separated by separator (defaults to none).

[1, 2, 3, 4, 5].join(", ") # => "1, 2, 3, 4, 5"

Prints to io the concatenation of the elements, with the possibility of controlling how the printing is done via a block.

[1, 2, 3, 4, 5].join(STDOUT, ", ") { |i, io| io << "(#{i})" }

Prints:

(1), (2), (3), (4), (5)

Prints to io the concatenation of the elements, with the possibility of controlling how the printing is done via a block.

[1, 2, 3, 4, 5].join(STDOUT, ", ") { |i, io| io << "(#{i})" }

Prints:

(1), (2), (3), (4), (5)

DEPRECATED Use #join(io : IO, separator = "", & : T, IO ->) instead

Returns a String created by concatenating the results of passing the elements in the collection to the passed block, separated by separator (defaults to none).

[1, 2, 3, 4, 5].join(", ") { |i| -i } # => "-1, -2, -3, -4, -5"

Returns an Array with the results of running the block against each element of the collection.

[1, 2, 3].map { |i| i * 10 } # => [10, 20, 30]

Like #map, but the block gets passed both the element and its index.

["Alice", "Bob"].map_with_index { |name, i| "User ##{i}: #{name}" }
# => ["User #0: Alice", "User #1: Bob"]

Accepts an optional offset parameter, which tells it to start counting from there.

Returns the element with the maximum value in the collection.

It compares using > so it will work for any type that supports that method.

[1, 2, 3].max        # => 3
["Alice", "Bob"].max # => "Bob"

Raises Enumerable::EmptyError if the collection is empty.

Like #max but returns nil if the collection is empty.

Returns the element for which the passed block returns with the maximum value.

It compares using > so the block must return a type that supports that method

["Alice", "Bob"].max_by { |name| name.size } # => "Alice"

Raises Enumerable::EmptyError if the collection is empty.

Like #max_by but returns nil if the collection is empty.

Like #max_by but instead of the element, returns the value returned by the block.

["Alice", "Bob"].max_of { |name| name.size } # => 5 (Alice's size)

Like #max_of but returns nil if the collection is empty.

Returns the element with the minimum value in the collection.

It compares using < so it will work for any type that supports that method.

[1, 2, 3].min        # => 1
["Alice", "Bob"].min # => "Alice"

Raises Enumerable::EmptyError if the collection is empty.

Like #min but returns nil if the collection is empty.

Returns the element for which the passed block returns with the minimum value.

It compares using < so the block must return a type that supports that method

["Alice", "Bob"].min_by { |name| name.size } # => "Bob"

Raises Enumerable::EmptyError if the collection is empty.

Like #min_by but returns nil if the collection is empty.

Like #min_by but instead of the element, returns the value returned by the block.

["Alice", "Bob"].min_of { |name| name.size } # => 3 (Bob's size)

Like #min_of but returns nil if the collection is empty.

Returns a Tuple with both the minimum and maximum value.

[1, 2, 3].minmax # => {1, 3}

Raises Enumerable::EmptyError if the collection is empty.

Like #minmax but returns {nil, nil} if the collection is empty.

Returns a Tuple with both the minimum and maximum values according to the passed block.

["Alice", "Bob", "Carl"].minmax_by { |name| name.size } # => {"Bob", "Alice"}

Raises Enumerable::EmptyError if the collection is empty.

Like #minmax_by but returns {nil, nil} if the collection is empty.

Returns a Tuple with both the minimum and maximum value the block returns when passed the elements in the collection.

["Alice", "Bob", "Carl"].minmax_of { |name| name.size } # => {3, 5}

Raises Enumerable::EmptyError if the collection is empty.

Like #minmax_of but returns {nil, nil} if the collection is empty.

Returns true if the passed block returns true for none of the elements of the collection.

[1, 2, 3].none? { |i| i > 5 } # => true

It's the opposite of #all?.

Returns true if pattern === element for no element in this enumerable.

[2, 3, 4].none?(5..7)      # => true
[2, "a", 3].none?(String)  # => false
%w[foo bar baz].none?(/e/) # => true

Returns true if all of the elements of the collection are false or nil.

[nil, false].none?       # => true
[nil, false, true].none? # => false

It's the opposite of #all?.

Returns true if the passed block returns true for exactly one of the elements of the collection.

[1, 2, 3].one? { |i| i > 2 } # => true
[1, 2, 3].one? { |i| i > 1 } # => false

Returns true if pattern === element for just one element in this enumerable.

[1, 10, 100].one?(7..14)   # => true
[2, "a", 3].one?(Int32)    # => false
%w[foo bar baz].one?(/oo/) # => true

Returns true if only one element in this enumerable is truthy.

[1, false, false].one? # => true
[1, false, 3].one?     # => false
[1].one?               # => true
[false].one?           # => false

Returns a Tuple with two arrays. The first one contains the elements in the collection for which the passed block returned true, and the second one those for which it returned false.

[1, 2, 3, 4, 5, 6].partition { |i| i % 2 == 0 } # => {[2, 4, 6], [1, 3, 5]}

Multiplies initial and all the elements in the collection together. The type of initial will be the type of the product, so use this if (for instance) you need to specify a large enough type to avoid overflow.

Expects all element types to respond to #* method.

[1, 2, 3, 4, 5, 6].product(7) # => 5040

If the collection is empty, returns initial.

([] of Int32).product(7) # => 7

Multiplies all the elements in the collection together.

Expects all element types to respond to #* method.

[1, 2, 3, 4, 5, 6].product # => 720

This method calls .multiplicative_identity on the element type to determine the type of the sum value.

If the collection is empty, returns multiplicative_identity.

([] of Int32).product # => 1

Multiplies initial and all results of the passed block for each element in the collection.

["Alice", "Bob"].product(2) { |name| name.size } # => 30 (2 * 5 * 3)

Expects all types returned from the block to respond to #* method.

If the collection is empty, returns 1.

([] of String).product(1) { |name| name.size } # => 1

Multiplies all results of the passed block for each element in the collection.

["Alice", "Bob"].product { |name| name.size } # => 15 (5 * 3)

Expects all types returned from the block to respond to #* method.

This method calls .multiplicative_identity on the element type to determine the type of the sum value.

If the collection is empty, returns multiplicative_identity.

([] of Int32).product { |x| x + 1 } # => 1

Just like the other variant, but you can set the initial value of the accumulator.

[1, 2, 3, 4, 5].reduce(10) { |acc, i| acc + i }             # => 25
[1, 2, 3].reduce([] of Int32) { |memo, i| memo.unshift(i) } # => [3, 2, 1]

Combines all elements in the collection by applying a binary operation, specified by a block, so as to reduce them to a single value.

For each element in the collection the block is passed an accumulator value (memo) and the element. The result becomes the new value for memo. At the end of the iteration, the final value of memo is the return value for the method. The initial value for the accumulator is the first element in the collection.

Raises Enumerable::EmptyError if the collection is empty.

[1, 2, 3, 4, 5].reduce { |acc, i| acc + i } # => 15

Similar to #reduce, but instead of raising when the input is empty, return nil

([] of Int32).reduce? { |acc, i| acc + i } # => nil

Returns an Array with all the elements in the collection for which the passed block returns false.

[1, 2, 3, 4, 5, 6].reject { |i| i % 2 == 0 } # => [1, 3, 5]

Returns an Array with all the elements in the collection that are not of the given type.

ints = [1, true, 3, false].reject(Bool)
ints         # => [1, 3]
typeof(ints) # => Array(Int32)

Returns an Array with all the elements in the collection for which pattern === element is false.

[1, 3, 2, 5, 4, 6].reject(3..5) # => [1, 2, 6]

Returns an Array of n random elements from self, using the given random number generator. All elements have equal probability of being drawn. Sampling is done without replacement; if n is larger than the size of this collection, the returned Array has the same size as self.

Raises ArgumentError if n is negative.

[1, 2, 3, 4, 5].sample(2)                # => [3, 5]
{1, 2, 3, 4, 5}.sample(2)                # => [3, 4]
{1, 2, 3, 4, 5}.sample(2, Random.new(1)) # => [1, 5]

Returns a random element from self, using the given random number generator. All elements have equal probability of being drawn.

Raises IndexError if self is empty.

a = [1, 2, 3]
a.sample                # => 2
a.sample                # => 1
a.sample(Random.new(1)) # => 3

Returns an Array with all the elements in the collection for which the passed block returns true.

[1, 2, 3, 4, 5, 6].select { |i| i % 2 == 0 } # => [2, 4, 6]

Returns an Array with all the elements in the collection that are of the given type.

ints = [1, true, nil, 3, false].select(Int32)
ints         # => [1, 3]
typeof(ints) # => Array(Int32)

Returns an Array with all the elements in the collection for which pattern === element.

[1, 3, 2, 5, 4, 6].select(3..5) # => [3, 5, 4]
["Alice", "Bob"].select(/^A/)   # => ["Alice"]

Returns the number of elements in the collection.

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

Returns an Array with the first count elements removed from the original collection.

If count is bigger than the number of elements in the collection, returns an empty array.

[1, 2, 3, 4, 5, 6].skip(3) # => [4, 5, 6]

Skips elements up to, but not including, the first element for which the block returns nil or false and returns an Array containing the remaining elements.

[1, 2, 3, 4, 5, 0].skip_while { |i| i < 3 } # => [3, 4, 5, 0]

Adds initial and all the elements in the collection together. The type of initial will be the type of the sum, so use this if (for instance) you need to specify a large enough type to avoid overflow.

Expects all element types to respond to #+ method.

[1, 2, 3, 4, 5, 6].sum(7) # => 28

If the collection is empty, returns initial.

([] of Int32).sum(7) # => 7

Adds all the elements in the collection together.

Expects all element types to respond to #+ method.

[1, 2, 3, 4, 5, 6].sum # => 21

This method calls .additive_identity on the yielded type to determine the type of the sum value.

If the collection is empty, returns additive_identity.

([] of Int32).sum # => 0

Adds initial and all results of the passed block for each element in the collection.

["Alice", "Bob"].sum(1) { |name| name.size } # => 9 (1 + 5 + 3)

Expects all types returned from the block to respond to #+ method.

If the collection is empty, returns initial.

([] of String).sum(1) { |name| name.size } # => 1

Adds all results of the passed block for each element in the collection.

["Alice", "Bob"].sum { |name| name.size } # => 8 (5 + 3)

Expects all types returned from the block to respond to #+ method.

This method calls .additive_identity on the yielded type to determine the type of the sum value.

If the collection is empty, returns additive_identity.

([] of Int32).sum { |x| x + 1 } # => 0

Passes elements to the block until the block returns nil or false, then stops iterating and returns an Array of all prior elements.

[1, 2, 3, 4, 5, 0].take_while { |i| i < 3 } # => [1, 2]

Tallies the collection. Returns a hash where the keys are the elements and the values are numbers of elements in the collection that correspond to the key.

["a", "b", "c", "b"].tally # => {"a"=>1, "b"=>2, "c"=>1}

Returns an Array with all the elements in the collection.

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

Creates a Hash out of an Enumerable where each element is a 2 element structure (for instance a Tuple or an Array).

[[:a, :b], [:c, :d]].to_h        # => {:a => :b, :c => :d}
Tuple.new({:a, 1}, {:c, 2}).to_h # => {:a => 1, :c => 2}

Creates a Hash out of Tuple pairs (key, value) returned from the block.

(1..3).to_h { |i| {i, i ** 2} } # => {1 => 1, 2 => 4, 3 => 9}

Returns a new Set with each unique element in the enumerable.

Yields elements of self and others in tandem to the given block.

Raises an IndexError if any of others doesn't have as many elements as self. See #zip? for a version that yields nil instead of raising.

a = [1, 2, 3]
b = ["a", "b", "c"]

a.zip(b) { |x, y| puts "#{x} -- #{y}" }

The above produces:

1 -- a
2 -- b
3 -- c

An example with multiple arguments:

(1..3).zip(4..6, 7..9) do |x, y, z|
  puts "#{x} -- #{y} -- #{z}"
end

The above produces:

1 -- 4 -- 7
2 -- 5 -- 8
3 -- 6 -- 9

Returns an Array of tuples populated with the elements of self and others traversed in tandem.

Raises an IndexError if any of others doesn't have as many elements as self. See #zip? for a version that yields nil instead of raising.

a = [1, 2, 3]
b = ["a", "b", "c"]

a.zip(b) # => [{1, "a"}, {2, "b"}, {3, "c"}]

An example with multiple arguments:

a = [1, 2, 3]
b = (4..6)
c = 8.downto(3)

a.zip(b, c) # => [{1, 4, 8}, {2, 5, 7}, {3, 6, 6}]

Yields elements of self and others in tandem to the given block.

All of the elements in self will be yielded: if others don't have that many elements they will be returned as nil.

a = [1, 2, 3]
b = ["a", "b"]

a.zip?(b) { |x, y| puts "#{x.inspect} -- #{y.inspect}" }

The above produces:

1 -- "a"
2 -- "b"
3 -- nil

An example with multiple arguments:

(1..3).zip?(4..5, 7..8) do |x, y, z|
  puts "#{x.inspect} -- #{y.inspect} -- #{z.inspect}"
end

The above produces:

1 -- 4 -- 7
2 -- 5 -- 8
3 -- nil -- nil

Returns an Array of tuples populated with the elements of self and others traversed in tandem.

All elements in self are returned in the Array. If matching elements in others are missing (because they don't have that many elements) nil is returned inside that tuple index.

a = [1, 2, 3]
b = ["a", "b"]

a.zip?(b) # => [{1, "a"}, {2, "b"}, {3, nil}]

An example with multiple arguments:

a = [1, 2, 3]
b = (4..5)
c = 8.downto(7)

a.zip?(b, c) # => [{1, 4, 8}, {2, 5, 7}, {3, nil, nil}]