要素を加える
先頭に追加 unshift
irb
>> arr = %w(た ま)
=> ["た", "ま"]
>> arr.unshift("あ") # 配列の先頭に要素を追加
=> ["あ", "た", "ま"]
末尾に追加 push
irb
>> arr = [1, 2]
=> [1, 2]
>> arr.push(3)
=> [1, 2, 3]
>> arr << 4 # arr.push(4) と同じ挙動
=> [1, 2, 3, 4]
連結
配列同士を連結 concat
irb
>> a = [1, 2]
=> [1, 2]
>> b = [3, 4]
=> [3, 4]
>> a.concat(b)
=> [1, 2, 3, 4]
要素を取り除く
要素がnilのものを取り除く compact
irb
>> a = [1, nil, 2]
=> [1, nil, 2]
>> a.compact
=> [1, 2]
配列から指定した要素を取り除く delete
irb
>> sushi = ["マグロ", "わさび"]
=> ["マグロ", "わさび"]
>> sushi.delete("わさび")
=> "わさび"
>> sushi
=> ["マグロ"] # わさびが取り除かれている
指定したインデックスの要素を取り除く delete_at
irb
>> arr = [1, 2, 3]
=> [1, 2, 3]
>> arr.delete_at(1)
=> 2
>> arr
=> [1, 3]
ブロックを評価しtrueの場合は要素を取り除く delete_if
irb
>> num = (1..10).to_a
=> [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
>> num.delete_if {|n| n % 2 == 0} # 偶数を取り除く
=> [1, 3, 5, 7, 9]
>> num
=> [1, 3, 5, 7, 9]
指定された部分を取り除き、取り除いた値を返す slice
irb
>> a = (1..5).to_a
=> [1, 2, 3, 4, 5]
>> a.slice(1, 3)
=> [2, 3, 4]
重複する要素を削除 uniq
irb
>> a = [1, 1, 2]
=> [1, 1, 2]
>> a.uniq
=> [1, 2]
先頭を取り除き、取り除いた値を返す shift
irb
>> a = ["頭", "胴体", "尻尾"]
=> ["頭", "胴体", "尻尾"]
>> a.shift
=> "頭"
>> a
=> ["胴体", "尻尾"]
末尾を取り除き、取り除いた値を返す pop
irb
>> a = ["a", "b", "\n"]
=> ["a", "b", "\n"]
>> a.pop
=> "\n"
>> a
=> ["a", "b"]
要素を置き換える
要素をブロックの条件に応じて置き換える collect, map
irb
>> name = ["Alice", "Bob"]
=> ["Alice", "Bob"]
>> name.map {|s| s + "-san"}
=> ["Alice-san", "Bob-san"]
要素を引数に応じて置き換える fill
irb
>> a = (1..5).to_a
=> [1, 2, 3, 4, 5]
>> a.fill(0)
=> [0, 0, 0, 0, 0]
irb
>> a = (1..5).to_a
=> [1, 2, 3, 4, 5]
>> a.fill("a", 1, 3) # インデックス1からスタートして要素3個分を"a"に置き換える
=> [1, "a", "a", "a", 5]
配列を平坦化(= 入れ子構造を解除)
irb
>> a = [1, [2, 3], [4, [5], 6]]
=> [1, [2, 3], [4, [5], 6]]
>> a.flatten
=> [1, 2, 3, 4, 5, 6]
要素を並べ替える
要素を逆順にする reverse
irb
>> a = (1..5).to_a
=> [1, 2, 3, 4, 5]
>> a.reverse
=> [5, 4, 3, 2, 1]
ブロックで指定した順番に並べ替え sort
irb
>> a = [2, 4, 0]
=> [2, 4, 0]
>> a.sort # 昇順
=> [0, 2, 4]
irb
>> words = %w(apple banana chocolate)
=> ["apple", "banana", "chocolate"]
>> words.sort {|a, b| a.length <=> b.length} # 長さの短い順
=> ["apple", "banana", "chocolate"]
>> words.sort {|a, b| b.length <=> a.length} # 長さの長い順
=> ["chocolate", "banana", "apple"]
ブロックで並べ替えの基準を決めてソートする sort_by
irb
>> words = ["aaa", "aa", "a"]
=> ["aaa", "aa", "a"]
>> words.sort_by {|w| w.length}
=> ["a", "aa", "aaa"]
参考