Hash

空のハッシュの生成

code:rb

Hash({}), {}, Hash.new, Hash[]

ハッシュの生成

code:rb

capital = {:Sweden =>"Stockholm", :Norway=>"Oslo", :Finland=>"Helsinki"}

capital = {Sweden: "Stockholm", Norway: "Oslo", Finland: "Helsinki"}

to_h（二次元配列からハッシュを作成）

code:rb

# => {1=>"data 1", 2=>"data 2"}

to_a （ハッシュとキーを一つの配列として2次元配列で返す）

code:rb

merge（ハッシュの結合）非破壊

code:rb

h1 = { "a" => 100, "b" => 200 }

h2 = { "b" => 246, "c" => 300 }

h1.merge!(h2)

# => { "a" => 100, "b" => 246, "c" => 300}

fetch（キーにマッチした値を取得する）

code:rb

fruits = { "apple" => 100, "orange" => 80}

puts fruits.fetch("apple")

update（）破壊的

code:rb

hash = {"apple" => "grate", "banana" => "ole", "orange" => "juice"}

hash.update({"grape" => "juice"})

values_at

code:rb

hash = {price: 100, order_code: 200, order_date: "2018/09/20", tax: 0.8}

p hash.values_at(:price, :tax)

invert （ハッシュの値とキーを入れ替える（重複した場合最後の値が優先される））非破壊的

code:rb

h = { "a" => 0, "b" => 100, "c" => 200, "d" => 300, "e" => 300 }

p h.invert

include・key・member

include?(key) -> bool

key?(key) -> bool

member?(key) -> bool

hash = {price: 100, order_code: 200, order_date: "2018/09/20", tax: 0.8}

p hash.