我有以下形式的哈希：
{ 1 => [], 2 => ["A", "B"], 3 => ["C"], 4 => ["B", "C"], 5 => ["D"] }
在 Ruby 中將其轉換為：
{ "A" => [2], "B" => [2, 4], "C" => [3, 4], "D" => [5], "default" => [1] }
uj5u.com熱心網友回復：
我知道的最好的方法。
hash = { 1 => [], 2 => ['A','B'], 3 => ['C'], 4 => ['B','C'], 5 => ['D'] }
new_hash = hash.inject({}) do |result, (key, values)|
values.each do |value|
result[value] ||= []
result[value].push(key)
end
result[:default] = [key] if values.empty?
result
end
puts new_hash
uj5u.com熱心網友回復：
一些更實用的方法：
array
.flat_map {|k,v| v.product([k])}
.group_by(&:first)
.transform_values {|v| v.map(&:last) }
uj5u.com熱心網友回復：
input = { 1 => [], 2 => ['A', 'B'], 3 => ['C'], 4 => ['B', 'C'], 5 => ['D'], 6 => [] }
output =
input.each_with_object(Hash.new([])) do |(key, values), hash|
values.each { |value| hash[value] = [key] }
hash['default'] = [key] if values.empty?
end
output
# => {"default"=>[1, 6], "A"=>[2], "B"=>[2, 4], "C"=>[3, 4], "D"=>[5]}
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