Ruby 配列

配列の生成

a = [1, 2, 3]
 => [1, 2, 3]
a.class
 => Array

Array[1, 2, 3]
 => [1, 2, 3]

Array.new(3, "str")
 => ["str", "str", "str"]

Array.new([1, 2, 3])
 => [1, 2, 3]

Array.new(5) {|i| i * 3}
 => [0, 3, 6, 9, 12]

配列に要素追加

a = [1, 2, 3]
 => [1, 2, 3]

<<メソッド

a << 4
 => [1, 2, 3, 4]

concatメソッド（破）

a.concat[5, 6]
 => [1, 2, 3, 4, 5, 6]

insertメソッド

a.insert(3, 9)
 => [1, 2, 3, 9, 4, 5, 6]

a.object_id
 => 47409483356240
b = a + [10]
 => [1, 2, 3, 9, 4, 5, 6, 10]
b.object_id
 => 47409481926320

unshiftメソッド

b.unshift(10) (破)
 => [10, 1, 2, 3, 9, 4, 5, 6, 10]

配列の要素変更

[]=メソッド

a = [1, 2, 3]
 => [1, 2, 3]
a[1] = 10
 => 10
a
 => [1, 10, 3]
a[1..2] = [10, 11]
 => [10, 11]
a
 => [1, 10, 11]
a[8] = 5
 => 5
a
 => [1, 10, 11, nil, nil, nil, nil, nil, 5]

fillメソッド

a = [1, 2, 3]
 => [1, 2, 3]
a.fill("s")
 => ["s", "s", "s"]
a.fill("t", 1..2)
 => ["s", "t", "t"]
a
 => ["s", "t", "t"]
a.fill(1..2){|index| index}
 => ["s", 1, 2]

replaceメソッド

a = [1, 2, 3]
 => [1, 2, 3]
a.object_id
 => 47409483213220
a.replace([4, 5, 6])
 => [4, 5, 6]
a.object_id
 => 47409483213220

配列の要素参照

a = [1, 2, 3]
 => [1, 2, 3]

[]メソッド

a[1]
 => 2
a[1..2]
 =>[2, 3]

atメソッド

a.at(1)
 => 2
#要素 < indexの場合、nilが返る

values_atメソッド

a.values_at(1)
 => [2]

fetchメソッド

a.fetch(4)
IndexError: index 4 outside of array bounds: -3...3
a.fetch 4, "ERROR"
 => "ERROR"
a.fetch(4){|n| "ERROR #{n}"}
 => "ERROR 4"

firstメソッド

a.first
 => 1
a.first(2)
 => [1, 2]

lastメソッド

a.last
 => 3

assocメソッド

a.assoc(3)
 => [3, 4]
#配列の配列を検索。最初の要素が指定された値と==で、その配列を返す。

rassocメソッド

a.rassoc(4)
 => [3, 4]
#index1の要素を検索。

配列の要素調べ

a = [1, 2, 3, 4, 5]
 => [1, 2, 3, 4, 5]

include?メソッド

a.include?(3)
 => true
a.include?(6)
 => false

indexメソッド

a.index(4)
 => 3
a.rindex(4)
 => 3
#該当しない場合、nilを返す。

配列の要素削除

a = [1, 2, 3, 4, 5]
 => [1, 2, 3, 4, 5]

delete_atメソッド

a.delete_at(2)
 => 3
a
 => [1, 2, 4, 5]

delete_ifメソッド

a = [1, 2, 3, 4, 5]
 => [1, 2, 3, 4, 5]
a.delete_if{|n| n % 2 == 0}
 => [1, 3, 5]

deleteメソッド

a = [1, 2, 3, 4, 5]
 => [1, 2, 3, 4, 5]
a.delete(3)
 => 3
a = [1, 2, 4, 5]
a.delete(10)
 => nil
a = [1, 2, 4, 5]

clearメソッド

a = [1, 2, 3, 4, 5]
 => [1, 2, 3, 4, 5]
a.clear
 => []

slice!メソッド

a = [1, 2, 3, 4, 5]
 => [1, 2, 3, 4, 5]
a.slice!(2, 2)
 => [3, 4]
a
 => [1, 2, 5]

shiftメソッド

a = [1, 2, 3, 4, 5]
 => [1, 2, 3, 4, 5]
a.shift(2)
 => [1, 2]
a.shift
 => 3
a
 => [4, 5]
#先頭から指定された数だけ要素を取り除いて返す。指定がなければ１。

popメソッド

a = [1, 2, 3, 4, 5]
 => [1, 2, 3, 4, 5]
a.pop(2)
 => [4, 5]
a.pop
 => 3
a
 => [1, 2]

- メソッド

a = [1, 2, 3, 4, 5]
 => [1, 2, 3, 4, 5]
a - [1, 2]
 => [3, 4, 5]
a - [1, 3, 5, 7]
 => [2, 4]

配列の演算

| メソッド

[1, 2, 3] | [1, 3, 5]
 => [1, 2, 3, 5]
#和集合

& メソッド

[1, 2, 3] & [1, 3, 5]
 => [1, 3]
#積集合

配列の比較

== メソッド

[1, 2, 3] == [1, 3, 5]
 => false
[1, 2, 3] <=> [1, 3, 5]
 => -1
#左辺が大きければ、0。右辺が大きければ-1。同じ0。