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comp.lang.ruby

Array comparison.. why does this work.

Jean Nibee

3/1/2007 2:46:00 AM

How does Ruby do Array comparision?

[code]
old_inventory = [ 'a', 'b', 'd' ]
new_inventory = [ 'a','e', 'c' ]

puts "The following files have been added: "
puts new_inventory - old_inventory
puts ""
puts "The following files have been deleted: "
puts old_inventory - new_inventory
[/code]

Notice the output is correct so it's not a case of element 0's being
compared in each array.

So...

Does Ruby sort arrays in memory first? or is a scan done 1 element at a
time?

Thanks.

--
Posted via http://www.ruby-....
2 Answers

dblack

3/1/2007 2:57:00 AM

0

Jean Nibee

3/1/2007 4:21:00 AM

0

>
> You're not doing comparison, though; you're doing subtraction.
> Subtraction doesn't depend on order. You can think of it as
> "without":
>
> [1,2,3] - [1] => [2,3] # [1,2,3] without 1
> [1,2,3,1] - [1] => [2,3] # [1,2,3,1] without 1
> [1,2,3] - [2] => [1,3] # [1,2,3] without 2
>
> etc.
>
>
> David

Sorry, when I mentioned comparison I meant "Under the hood". (I realise
'-' is subtractions ), but the interpreter needs to perform comparisoin
to see if an element exists somewhere.

I was curious if it just interates through one array looking for that
element in the second, or does it (internally) sort the array, iterate
each array performing comparision and if a > b skipping the equality
determination to save CPU cycles and doing a 'next'.

I guess what I"m saying (Makes more sense when you see pseudo code) is
how does it work in the interpreter.

--
Posted via http://www.ruby-....