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  • * in { |key, value| value * 2 }

    From dreamer@21:1/5 to All on Mon Jul 8 15:24:53 2019
    Hi all,
    I'm new to ruby and trying to understand this bit of code:

    hash.update(hash) { |key, value| value * 2}

    In particular what is the meaning of the value * 2?

    When I tried using IRB to multiply values in a hash, either
    I received an error or it multiplied the values and gave me
    the product.

    Any insights would be greatly appreciated. Thank you.


    --
    --
    danny lee <[email protected]> (fka [email protected], [email protected])

    "I remarked to Dennis [Ritchie] that easily half the code I was writing in Multics was error recovery code. He said, "We left all that stuff out [of Unix]. If there's an error, we have this routine called panic, and when it
    is called, the machine crashes, and you holler down the hall, 'Hey, reboot it.'"- Tom Van Vleck.

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  • From Doc O'Leary@21:1/5 to dreamer on Sun Jul 14 15:44:57 2019
    For your reference, records indicate that
    dreamer <[email protected]> wrote:

    hash.update(hash) { |key, value| value * 2}

    In particular what is the meaning of the value * 2?

    It means the same thing it would mean anywhere else: multiply the contents
    of the “value” variable by 2. Is it really blocks that have you confused, or the use of the update method? For newer versions of Ruby, the other
    choice to do the same operation would be the transform_values! method.

    When I tried using IRB to multiply values in a hash, either
    I received an error or it multiplied the values and gave me
    the product.

    You show no examples, errors or otherwise. The line you posted should do
    what I *think* you want, but you many need to explain your intent more completely.

    --
    "Also . . . I can kill you with my brain."
    River Tam, Trash, Firefly

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  • From dreamer@21:1/5 to Doc O'Leary on Tue Jul 16 15:27:42 2019
    Doc O'Leary <[email protected]> wrote:
    For your reference, records indicate that
    dreamer <[email protected]> wrote:

    hash.update(hash) { |key, value| value * 2}

    In particular what is the meaning of the value * 2?

    It means the same thing it would mean anywhere else: multiply the contents
    of the “value” variable by 2. Is it really blocks that have you confused,
    or the use of the update method? For newer versions of Ruby, the other choice to do the same operation would be the transform_values! method.

    When I tried using IRB to multiply values in a hash, either
    I received an error or it multiplied the values and gave me
    the product.

    You show no examples, errors or otherwise. The line you posted should do what I *think* you want, but you many need to explain your intent more completely.



    Sorry, that was bad netiquette on my part. I sometimes get focused on my
    own thoughts and understanding and don't speak (or write) in a way that fully explains the situation to an outside observer.

    Here is an example I found on stackoverflow (https://stackoverflow.com/questions/5215713/ruby-what-is-the-easiest-method-to-update-hash-values)

    h = { 1 => 10, 2 => 20, 5 => 70, 8 =>90, 4 => 34 }

    which the writer would like to change to:

    h = { 1 => foo(10), 2 => foo(20), 5 => foo(70), 8 => foo(90), 4 => foo(34) }

    and the "best" answer was the line above:

    hash.update(hash) { |key, value| value * 2 }

    My confusion was really about the "value * 2", the answer's author wrote:

    "Note that we're effectively merging hash with itself. This is
    needed because Ruby will call the block to resolve the merge
    for any keys that collide, setting the value with the return
    value of the block."

    I was wondering why this would be better/different than just doing an
    update to the hash and key. And what is meant by 'resolving the merge
    for any keys that collide'.


    I was confused about blocks AND how to use the update method, but
    this bit had me doubly confused.

    Now that I've had time to step and back and think about it, I may just
    be overthinking and this bit of code could be meaningless, in a sense.





    --
    --
    danny lee <[email protected]>

    "Every artist was first an amateur." - Ralph Waldo Emerson

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  • From Doc O'Leary@21:1/5 to dreamer on Tue Jul 16 19:44:20 2019
    For your reference, records indicate that
    dreamer <[email protected]> wrote:

    Here is an example I found on stackoverflow (https://stackoverflow.com/questions/5215713/ruby-what-is-the-easiest-method-to-update-hash-values)

    h = { 1 => 10, 2 => 20, 5 => 70, 8 =>90, 4 => 34 }

    which the writer would like to change to:

    h = { 1 => foo(10), 2 => foo(20), 5 => foo(70), 8 => foo(90), 4 => foo(34) }

    and the "best" answer was the line above:

    hash.update(hash) { |key, value| value * 2 }

    My confusion was really about the "value * 2"

    Well, in that case the answer did confuse the issue a bit by giving that instead of “foo(value)” to correspond with the question.

    "Note that we're effectively merging hash with itself. This is
    needed because Ruby will call the block to resolve the merge
    for any keys that collide, setting the value with the return
    value of the block."

    I was wondering why this would be better/different than just doing an
    update to the hash and key.

    By doing what instead? You certain *could* just iterate through using an enumerator, making assignments explicitly. But using a block with the
    update method is a much more convenient way to accomplish the task (and generally why so many generic Enumerable methods accept blocks).

    And what is meant by 'resolving the merge
    for any keys that collide'.

    That’s just the way the update method works. Its “normal” use is to merge
    two different hashes, and the block is only run to resolve the case where
    there are keys that exist in both. But used against itself, *all* entries
    will match, and thus be changed by the code in the given block.

    --
    "Also . . . I can kill you with my brain."
    River Tam, Trash, Firefly

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  • From dreamer@21:1/5 to Doc O'Leary on Wed Jul 17 23:21:49 2019
    Doc O'Leary <[email protected]> wrote:
    For your reference, records indicate that
    dreamer <[email protected]> wrote:


    That’s just the way the update method works. Its “normal” use is to merge
    two different hashes, and the block is only run to resolve the case where there are keys that exist in both. But used against itself, *all* entries will match, and thus be changed by the code in the given block.


    Thank you for the clarification. I appreciate you taking the time to
    respond and give me a better understanding of this. I'm finding Ruby
    intuitive and, may I say, "fun" :)




    .------------------( Danny Lee <[email protected]> )------------------.
    I have been impressed with the urgency of doing. Knowing is not enough;
    we must apply. Being willing is not enough; we must do.
    ~ Leonardo da Vinci

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