Ruby/Справочник/Enumerable
Материал из Викиучебника
[править] Примесь Enumerable
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.
Методы объекта
all?, any?, collect, detect, each_cons, each_slice, each_with_index, entries, enum_cons, enum_slice, enum_with_index, find_all, find, grep, group_by, include?, index_by, inject, map, max, member?, min, partition, reject, select, sort_by, sort, sum, to_a, to_set, zip
[править] Enumerable#all?
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
[править] Enumerable#any?
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
[править] Enumerable#collect
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"]
[править] Enumerable#detect
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
[править] Enumerable#each_cons
each_cons(n) {...}
Iterates the given block for each array of consecutive <n> elements. 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]
[править] Enumerable#each_slice
e.each_slice(n) {...}
Iterates the given block for each slice of <n> elements. e.g.:
(1..10).each_slice(3) {|a| p a}
# outputs below
[1, 2, 3]
[4, 5, 6]
[7, 8, 9]
[10]
[править] Enumerable#each_with_index
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}
[править] Enumerable#entries
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]]
[править] Enumerable#enum_cons
e.enum_cons(n)
Returns Enumerable::Enumerator.new(self, :each_cons, n).
[править] Enumerable#enum_slice
e.enum_slice(n)
Returns Enumerable::Enumerator.new(self, :each_slice, n).
[править] Enumerable#enum_with_index
enum_with_index
Returns Enumerable::Enumerator.new(self, :each_with_index).
[править] Enumerable#find
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
[править] Enumerable#find_all
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]
[править] Enumerable#grep
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]
[править] Enumerable#group_by
group_by() {|element| ...}
Collect an enumerable into sets, grouped by the result of a block. Useful, for example, for grouping records by date. e.g.
latest_transcripts.group_by(&:day).each do |day, transcripts|
p "#{day} -> #{transcripts.map(&:class) * ', '}"
end
"2006-03-01 -> Transcript"
"2006-02-28 -> Transcript"
"2006-02-27 -> Transcript, Transcript"
"2006-02-26 -> Transcript, Transcript"
"2006-02-25 -> Transcript"
"2006-02-24 -> Transcript, Transcript"
"2006-02-23 -> Transcript"
[править] Enumerable#include?
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
[править] Enumerable#index_by
index_by() {|elem| ...}
Convert an enumerable to a hash. Examples:
people.index_by(&:login)
=> { "nextangle" => <Person ...>, "chade-" => <Person ...>, ...}
people.index_by { |person| "#{person.first_name} #{person.last_name}" }
=> { "Chade- Fowlersburg-e" => <Person ...>, "David Heinemeier Hansson" => <Person ...>, ...}
[править] Enumerable#inject
enum.inject(initial) {| memo, obj | block } => obj
enum.inject {| memo, obj | block } => obj
Combines the elements of enum by applying the block to an accumulator value (memo) and each element in turn. At each step, memo is set to the value returned by the block. The first form lets you supply an initial value for memo. The second form uses the first element of the collection as a the initial value (and skips that element while iterating).
# Sum some numbers
(5..10).inject {|sum, n| sum + n } #=> 45
# Multiply some numbers
(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"
# find the length of the longest word
longest = %w{ cat sheep bear }.inject(0) do |memo,word|
memo >= word.length ? memo : word.length
end
longest #=> 5
[править] Enumerable#map
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"]
[править] Enumerable#max
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"
[править] Enumerable#member?
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
[править] Enumerable#min
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"
[править] Enumerable#partition
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]]
[править] Enumerable#reject
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]
[править] Enumerable#select
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]
[править] Enumerable#sort
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]
[править] Enumerable#sort_by
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"]
[править] Enumerable#sum
sum(identity = 0, &block)
Calculates a sum from the elements. Examples:
payments.sum { |p| p.price * p.tax_rate }
payments.sum(&:price)
This is instead of payments.inject { |sum, p| sum + p.price } Also calculates sums without the use of a block:
[5, 15, 10].sum # => 30
The default identity (sum of an empty list) is zero. However, you can override this default: [].sum(Payment.new(0)) { |i| i.amount } # => Payment.new(0)
[править] Enumerable#to_a
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]]
[править] Enumerable#to_set
to_set(klass = Set, *args, &block)
Makes a set from the enumerable object with given arguments. Needs to +require "set"+ to use this method.
[править] Enumerable#zip
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]]
