Feature #5550

Hash#depth, Hash#flat_length for recursive hashes

Added by Tsuyoshi Sawada over 2 years ago. Updated over 1 year ago.

[ruby-dev:44776]
Status:Rejected
Priority:Normal
Assignee:-
Category:-
Target version:-

Description

I often have a hash whose value is recursively a hash, which may look like the following:

{"Japan" =>
    {"Hokkaido" => "Sapporo", ...},
    {"Honhuu" =>
        {"Aomori" => "Hirosaki", ...},
        {"Akita" => ...},
        ...
    },
    {"Shikoku" => ...},
    ...
}

In these cases, it will be convenient if there is a way to know the (maximum) depth of he original hash, and the numbers of all the "terminal nodes". I would like to propose two methods Hash#depth and Hash#flat_length, whose Ruby implementation can be as follows:

class Hash
def depth
    1 + (values.map{|v| Hash === v ? v.depth : 1}.max)
end
def flat_length
    values.inject(0){|sum, v| sum + (Hash === v ? v.flat_length : 1)}
end
end

History

#1 Updated by Yukihiro Matsumoto over 2 years ago

  • Status changed from Open to Feedback

Hashの本質はkey-valueのマッピングなので、valueが再帰的にHashであることを想定した(再帰的なHashでなければ役に立たない)メソッドを追加することには抵抗があります。
わずか6行のmonkey patchingを避けるためにすべてのRubyに追加すべきメソッドですか?

#2 Updated by Alexey Muranov over 2 years ago

Excuse me, can you be more precise with your example please? Ruby does not accept it (after removing the dots "..."). Are you talking about nested hashes? How about creating a class Tree that would inherit from Hash and define additional methods there?

#3 Updated by Thomas Sawyer over 2 years ago

I take it you meant nested hash. I think your methods will infinite loop on recursive hash --and that needs to be considered.

I understand #depth, Array might use such a method too. But #flat_length, I don't quite get what is being counted.

#4 Updated by Yusuke Endoh over 1 year ago

  • Status changed from Feedback to Rejected

No feedback, looks hopeless to me. Closing.

Yusuke Endoh mame@tsg.ne.jp

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