- Inheritance
The Enumerable mixin provides collection classes with several traversal and searching methods, and with the ability to sort. The class must provide a method each, which yields successive members of the collection. If Enumerable#max, min, or sort is used, the objects in the collection must also implement a meaningful <=> operator, as these methods rely on an ordering between members of the collection.
Classes & Modules
Methods
Instance
| Visibility | Signature |
|---|---|
| public | all? () |
| public | any? () |
| public | collect () |
| public | count (...) |
| public | cycle (...) |
| public | detect (...) |
| public | drop (p1) |
| public | drop_while () |
| public | each_cons (p1) |
| public | each_slice (p1) |
| public | each_with_index () |
| public | entries (...) |
| public | enum_cons (p1) |
| public | enum_slice (p1) |
| public | enum_with_index () |
| public | find (...) |
| public | find_all () |
| public | find_index (...) |
| public | first (...) |
| public | grep (p1) |
| public | group_by () |
| public | include? (p1) |
| public | inject (init) {|result, item| ...} |
| public | inject (...) |
| public | map () |
| public | max () |
| public | max_by () |
| public | member? (p1) |
| public | min () |
| public | min_by () |
| public | minmax () |
| public | minmax_by () |
| public | none? () |
| public | one? () |
| public | partition () |
| public | reduce (...) |
| public | reject () |
| public | reverse_each (...) |
| public | select () |
| public | sort () |
| public | sort_by () |
| public | take (p1) |
| public | take_while () |
| public | to_a (...) |
| public | to_set (klass = Set, *args, &block) |
| public | zip (...) |
Instance Method Detail
enum.all? [{|obj| block } ] => true or false
Passes each element of the collection to the given block. The method returns true if the block never returns false or nil. If the block is not given, Ruby adds an implicit block of {|obj| obj} (that is all? will return true only if none of the collection members are false or nil.)
%w{ ant bear cat}.all? {|word| word.length >= 3} #=> true
%w{ ant bear cat}.all? {|word| word.length >= 4} #=> false
[ nil, true, 99 ].all? #=> false
enum.any? [{|obj| block } ] => true or false
Passes each element of the collection to the given block. The method returns true if the block ever returns a value other than false or nil. If the block is not given, Ruby adds an implicit block of {|obj| obj} (that is any? will return true if at least one of the collection members is not false or nil.
%w{ ant bear cat}.any? {|word| word.length >= 3} #=> true
%w{ ant bear cat}.any? {|word| word.length >= 4} #=> true
[ nil, true, 99 ].any? #=> true
enum.collect {| obj | block } => array
enum.map {| obj | block } => array
Returns a new array with the results of running block once for every element in enum.
(1..4).collect {|i| i*i } #=> [1, 4, 9, 16]
(1..4).collect { "cat" } #=> ["cat", "cat", "cat", "cat"]
enum.count => int
enum.count(item) => int
enum.count {| obj | block } => int
Returns the number of items in enum, where size is called if it responds to it, otherwise the items are counted through enumeration. If an argument is given, counts the number of items in enum, for which equals to item. If a block is given, counts the number of elements yielding a true value.
ary = [1, 2, 4, 2]
ary.count # => 4
ary.count(2) # => 2
ary.count{|x|x%2==0} # => 3
enum.cycle {|obj| block }
enum.cycle(n) {|obj| block }
Calls block for each element of enum repeatedly n times or forever if none or nil is given. If a non-positive number is given or the collection is empty, does nothing. Returns nil if the loop has finished without getting interrupted.
Enumerable#cycle saves elements in an internal array so changes to enum after the first pass have no effect.
a = ["a", "b", "c"]
a.cycle {|x| puts x } # print, a, b, c, a, b, c,.. forever.
a.cycle(2) {|x| puts x } # print, a, b, c, a, b, c.
enum.detect(ifnone = nil) {| obj | block } => obj or nil
enum.find(ifnone = nil) {| obj | block } => obj or nil
Passes each entry in enum to block. Returns the first for which block is not false. If no object matches, calls ifnone and returns its result when it is specified, or returns nil
(1..10).detect {|i| i % 5 == 0 and i % 7 == 0 } #=> nil
(1..100).detect {|i| i % 5 == 0 and i % 7 == 0 } #=> 35
enum.drop(n) => array
Drops first n elements from enum, and returns rest elements in an array.
a = [1, 2, 3, 4, 5, 0] a.drop(3) # => [4, 5, 0]
enum.drop_while {|arr| block } => array
Drops 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.
a = [1, 2, 3, 4, 5, 0]
a.drop_while {|i| i < 3 } # => [3, 4, 5, 0]
each_cons(n) {...}
each_cons(n)
Iterates the given block for each array of consecutive <n> elements. If no block is given, returns an enumerator.a
e.g.:
(1..10).each_cons(3) {|a| p a}
# outputs below
[1, 2, 3]
[2, 3, 4]
[3, 4, 5]
[4, 5, 6]
[5, 6, 7]
[6, 7, 8]
[7, 8, 9]
[8, 9, 10]
e.each_slice(n) {...}
e.each_slice(n)
Iterates the given block for each slice of <n> elements. If no block is given, returns an enumerator.
e.g.:
(1..10).each_slice(3) {|a| p a}
# outputs below
[1, 2, 3]
[4, 5, 6]
[7, 8, 9]
[10]
enum.each_with_index {|obj, i| block } → enum
Calls block with two arguments, the item and its index, for each item in enum.
hash = Hash.new
%w(cat dog wombat).each_with_index {|item, index|
hash[item] = index
}
hash #=> {"cat"=>0, "wombat"=>2, "dog"=>1}
enum.to_a => array
enum.entries => array
Returns an array containing the items in enum.
(1..7).to_a #=> [1, 2, 3, 4, 5, 6, 7]
{ 'a'=>1, 'b'=>2, 'c'=>3 }.to_a #=> [["a", 1], ["b", 2], ["c", 3]]
each_cons(n) {...}
each_cons(n)
Iterates the given block for each array of consecutive <n> elements. If no block is given, returns an enumerator.a
e.g.:
(1..10).each_cons(3) {|a| p a}
# outputs below
[1, 2, 3]
[2, 3, 4]
[3, 4, 5]
[4, 5, 6]
[5, 6, 7]
[6, 7, 8]
[7, 8, 9]
[8, 9, 10]
e.each_slice(n) {...}
e.each_slice(n)
Iterates the given block for each slice of <n> elements. If no block is given, returns an enumerator.
e.g.:
(1..10).each_slice(3) {|a| p a}
# outputs below
[1, 2, 3]
[4, 5, 6]
[7, 8, 9]
[10]
enum.each_with_index {|obj, i| block } → enum
Calls block with two arguments, the item and its index, for each item in enum.
hash = Hash.new
%w(cat dog wombat).each_with_index {|item, index|
hash[item] = index
}
hash #=> {"cat"=>0, "wombat"=>2, "dog"=>1}
enum.detect(ifnone = nil) {| obj | block } => obj or nil
enum.find(ifnone = nil) {| obj | block } => obj or nil
Passes each entry in enum to block. Returns the first for which block is not false. If no object matches, calls ifnone and returns its result when it is specified, or returns nil
(1..10).detect {|i| i % 5 == 0 and i % 7 == 0 } #=> nil
(1..100).detect {|i| i % 5 == 0 and i % 7 == 0 } #=> 35
enum.find_all {| obj | block } => array
enum.select {| obj | block } => array
Returns an array containing all elements of enum for which block is not false (see also Enumerable#reject).
(1..10).find_all {|i| i % 3 == 0 } #=> [3, 6, 9]
enum.find_index(value) => int or nil
enum.find_index {| obj | block } => int or nil
Compares each entry in enum with value or passes to block. Returns the index for the first for which the evaluated value is non-false. If no object matches, returns nil
(1..10).find_index {|i| i % 5 == 0 and i % 7 == 0 } #=> nil
(1..100).find_index {|i| i % 5 == 0 and i % 7 == 0 } #=> 34
(1..100).find_index(50) #=> 49
enum.first → obj or nil
enum.first(n) → an_array
Returns the first element, or the first n elements, of the enumerable. If the enumerable is empty, the first form returns nil, and the second form returns an empty array.
enum.grep(pattern) => array
enum.grep(pattern) {| obj | block } => array
Returns an array of every element in enum for which Pattern === element. If the optional block is supplied, each matching element is passed to it, and the block‘s result is stored in the output array.
(1..100).grep 38..44 #=> [38, 39, 40, 41, 42, 43, 44]
c = IO.constants
c.grep(/SEEK/) #=> ["SEEK_END", "SEEK_SET", "SEEK_CUR"]
res = c.grep(/SEEK/) {|v| IO.const_get(v) }
res #=> [2, 0, 1]
enum.group_by {| obj | block } => a_hash
Returns a hash, which keys are evaluated result from the block, and values are arrays of elements in enum corresponding to the key.
(1..6).group_by {|i| i%3} #=> {0=>[3, 6], 1=>[1, 4], 2=>[2, 5]}
enum.include?(obj) => true or false
enum.member?(obj) => true or false
Returns true if any member of enum equals obj. Equality is tested using ==.
IO.constants.include? "SEEK_SET" #=> true IO.constants.include? "SEEK_NO_FURTHER" #=> false
inject(init) {|result, item| ...}
enum.inject(initial, sym) => obj
enum.inject(sym) => obj
enum.inject(initial) {| memo, obj | block } => obj
enum.inject {| memo, obj | block } => obj
enum.reduce(initial, sym) => obj
enum.reduce(sym) => obj
enum.reduce(initial) {| memo, obj | block } => obj
enum.reduce {| memo, obj | block } => obj
Combines all elements of enum by applying a binary operation, specified by a block or a symbol that names a method or operator.
If you specify a block, then for each element in enum<i> the block is passed an accumulator value (<i>memo) and the element. If you specify a symbol instead, then each element in the collection will be passed to the named method of memo. In either case, the result becomes the new value for memo. At the end of the iteration, the final value of memo is the return value fo the method.
If you do not explicitly specify an initial value for memo, then uses the first element of collection is used as the initial value of memo.
Examples:
# Sum some numbers
(5..10).reduce(:+) #=> 45
# Same using a block and inject
(5..10).inject {|sum, n| sum + n } #=> 45
# Multiply some numbers
(5..10).reduce(1, :*) #=> 151200
# Same using a block
(5..10).inject(1) {|product, n| product * n } #=> 151200
# find the longest word
longest = %w{ cat sheep bear }.inject do |memo,word|
memo.length > word.length ? memo : word
end
longest #=> "sheep"
enum.collect {| obj | block } => array
enum.map {| obj | block } => array
Returns a new array with the results of running block once for every element in enum.
(1..4).collect {|i| i*i } #=> [1, 4, 9, 16]
(1..4).collect { "cat" } #=> ["cat", "cat", "cat", "cat"]
enum.max => obj
enum.max {|a,b| block } => obj
Returns the object in enum with the maximum value. The first form assumes all objects implement Comparable; the second uses the block to return a <=> b.
a = %w(albatross dog horse)
a.max #=> "horse"
a.max {|a,b| a.length <=> b.length } #=> "albatross"
enum.max_by {| obj| block } => obj
Returns the object in enum that gives the maximum value from the given block.
a = %w(albatross dog horse)
a.max_by {|x| x.length } #=> "albatross"
enum.include?(obj) => true or false
enum.member?(obj) => true or false
Returns true if any member of enum equals obj. Equality is tested using ==.
IO.constants.include? "SEEK_SET" #=> true IO.constants.include? "SEEK_NO_FURTHER" #=> false
enum.min => obj
enum.min {| a,b | block } => obj
Returns the object in enum with the minimum value. The first form assumes all objects implement Comparable; the second uses the block to return a <=> b.
a = %w(albatross dog horse)
a.min #=> "albatross"
a.min {|a,b| a.length <=> b.length } #=> "dog"
enum.min_by {| obj| block } => obj
Returns the object in enum that gives the minimum value from the given block.
a = %w(albatross dog horse)
a.min_by {|x| x.length } #=> "dog"
enum.minmax => [min,max]
enum.minmax {|a,b| block } => [min,max]
Returns two elements array which contains the minimum and the maximum value in the enumerable. The first form assumes all objects implement Comparable; the second uses the block to return a <=> b.
a = %w(albatross dog horse)
a.minmax #=> ["albatross", "horse"]
a.minmax {|a,b| a.length <=> b.length } #=> ["dog", "albatross"]
enum.minmax_by {| obj| block } => [min, max]
Returns two elements array array containing the objects in enum that gives the minimum and maximum values respectively from the given block.
a = %w(albatross dog horse)
a.minmax_by {|x| x.length } #=> ["dog", "albatross"]
enum.none? [{|obj| block }] => true or false
Passes each element of the collection to the given block. The method returns true if the block never returns true for all elements. If the block is not given, none? will return true only if none of the collection members is true.
%w{ant bear cat}.none? {|word| word.length == 5} #=> true
%w{ant bear cat}.none? {|word| word.length >= 4} #=> false
[].none? #=> true
[nil].none? #=> true
[nil,false].none? #=> true
enum.one? [{|obj| block }] => true or false
Passes each element of the collection to the given block. The method returns true if the block returns true exactly once. If the block is not given, one? will return true only if exactly one of the collection members is true.
%w{ant bear cat}.one? {|word| word.length == 4} #=> true
%w{ant bear cat}.one? {|word| word.length > 4} #=> false
%w{ant bear cat}.one? {|word| word.length < 4} #=> false
[ nil, true, 99 ].one? #=> false
[ nil, true, false ].one? #=> true
enum.partition {| obj | block } => [ true_array, false_array ]
Returns two arrays, the first containing the elements of enum for which the block evaluates to true, the second containing the rest.
(1..6).partition {|i| (i&1).zero?} #=> [[2, 4, 6], [1, 3, 5]]
enum.inject(initial, sym) => obj
enum.inject(sym) => obj
enum.inject(initial) {| memo, obj | block } => obj
enum.inject {| memo, obj | block } => obj
enum.reduce(initial, sym) => obj
enum.reduce(sym) => obj
enum.reduce(initial) {| memo, obj | block } => obj
enum.reduce {| memo, obj | block } => obj
Combines all elements of enum by applying a binary operation, specified by a block or a symbol that names a method or operator.
If you specify a block, then for each element in enum<i> the block is passed an accumulator value (<i>memo) and the element. If you specify a symbol instead, then each element in the collection will be passed to the named method of memo. In either case, the result becomes the new value for memo. At the end of the iteration, the final value of memo is the return value fo the method.
If you do not explicitly specify an initial value for memo, then uses the first element of collection is used as the initial value of memo.
Examples:
# Sum some numbers
(5..10).reduce(:+) #=> 45
# Same using a block and inject
(5..10).inject {|sum, n| sum + n } #=> 45
# Multiply some numbers
(5..10).reduce(1, :*) #=> 151200
# Same using a block
(5..10).inject(1) {|product, n| product * n } #=> 151200
# find the longest word
longest = %w{ cat sheep bear }.inject do |memo,word|
memo.length > word.length ? memo : word
end
longest #=> "sheep"
enum.reject {| obj | block } => array
Returns an array for all elements of enum for which block is false (see also Enumerable#find_all).
(1..10).reject {|i| i % 3 == 0 } #=> [1, 2, 4, 5, 7, 8, 10]
enum.reverse_each {|item| block }
Traverses enum in reverse order.
enum.find_all {| obj | block } => array
enum.select {| obj | block } => array
Returns an array containing all elements of enum for which block is not false (see also Enumerable#reject).
(1..10).find_all {|i| i % 3 == 0 } #=> [3, 6, 9]
enum.sort => array
enum.sort {| a, b | block } => array
Returns an array containing the items in enum sorted, either according to their own <=> method, or by using the results of the supplied block. The block should return -1, 0, or +1 depending on the comparison between a and b. As of Ruby 1.8, the method Enumerable#sort_by implements a built-in Schwartzian Transform, useful when key computation or comparison is expensive..
%w(rhea kea flea).sort #=> ["flea", "kea", "rhea"]
(1..10).sort {|a,b| b <=> a} #=> [10, 9, 8, 7, 6, 5, 4, 3, 2, 1]
enum.sort_by {| obj | block } => array
Sorts enum using a set of keys generated by mapping the values in enum through the given block.
%w{ apple pear fig }.sort_by {|word| word.length}
#=> ["fig", "pear", "apple"]
The current implementation of sort_by generates an array of tuples containing the original collection element and the mapped value. This makes sort_by fairly expensive when the keysets are simple
require 'benchmark'
include Benchmark
a = (1..100000).map {rand(100000)}
bm(10) do |b|
b.report("Sort") { a.sort }
b.report("Sort by") { a.sort_by {|a| a} }
end
produces:
user system total real Sort 0.180000 0.000000 0.180000 ( 0.175469) Sort by 1.980000 0.040000 2.020000 ( 2.013586)
However, consider the case where comparing the keys is a non-trivial operation. The following code sorts some files on modification time using the basic sort method.
files = Dir["*"]
sorted = files.sort {|a,b| File.new(a).mtime <=> File.new(b).mtime}
sorted #=> ["mon", "tues", "wed", "thurs"]
This sort is inefficient: it generates two new File objects during every comparison. A slightly better technique is to use the Kernel#test method to generate the modification times directly.
files = Dir["*"]
sorted = files.sort { |a,b|
test(?M, a) <=> test(?M, b)
}
sorted #=> ["mon", "tues", "wed", "thurs"]
This still generates many unnecessary Time objects. A more efficient technique is to cache the sort keys (modification times in this case) before the sort. Perl users often call this approach a Schwartzian Transform, after Randal Schwartz. We construct a temporary array, where each element is an array containing our sort key along with the filename. We sort this array, and then extract the filename from the result.
sorted = Dir["*"].collect { |f|
[test(?M, f), f]
}.sort.collect { |f| f[1] }
sorted #=> ["mon", "tues", "wed", "thurs"]
This is exactly what sort_by does internally.
sorted = Dir["*"].sort_by {|f| test(?M, f)}
sorted #=> ["mon", "tues", "wed", "thurs"]
enum.take(n) => array
Returns first n elements from enum.
a = [1, 2, 3, 4, 5, 0] a.take(3) # => [1, 2, 3]
enum.take_while {|arr| block } => array
Passes elements to the block until the block returns nil or false, then stops iterating and returns an array of all prior elements.
a = [1, 2, 3, 4, 5, 0]
a.take_while {|i| i < 3 } # => [1, 2]
enum.to_a => array
enum.entries => array
Returns an array containing the items in enum.
(1..7).to_a #=> [1, 2, 3, 4, 5, 6, 7]
{ 'a'=>1, 'b'=>2, 'c'=>3 }.to_a #=> [["a", 1], ["b", 2], ["c", 3]]
to_set(klass = Set, *args, &block)
Makes a set from the enumerable object with given arguments. Needs to +require "set"+ to use this method.
enum.zip(arg, ...) => array
enum.zip(arg, ...) {|arr| block } => nil
Converts any arguments to arrays, then merges elements of enum with corresponding elements from each argument. This generates a sequence of enum#size n-element arrays, where n is one more that the count of arguments. If the size of any argument is less than enum#size, nil values are supplied. If a block given, it is invoked for each output array, otherwise an array of arrays is returned.
a = [ 4, 5, 6 ] b = [ 7, 8, 9 ] (1..3).zip(a, b) #=> [[1, 4, 7], [2, 5, 8], [3, 6, 9]] "cat\ndog".zip([1]) #=> [["cat\n", 1], ["dog", nil]] (1..3).zip #=> [[1], [2], [3]]