From: shadowfirebird@...
Date: 2008-08-01T22:01:28+09:00
Subject: Re: Using array.select with grep

Someone please correct me if I'm barking up the wrong tree, but the
block in select wants a function that returns a logical, and grep
isn't one.

It seems to work if you use include?(), instead, though.

irb(main):004:0> a1 = [ "one", "two", "three" ]
=> ["one", "two", "three"]
irb(main):005:0> a2 = ["two", "three", "four" ]
=> ["two", "three", "four"]
irb(main):006:0> a1.find_all{|x| a2.grep(x)}
=> ["one", "two", "three"]
irb(main):007:0> a1.find_all{|x| a2.grep(x) == true}
=> []
irb(main):007:0> a1.find_all{|x| a2.include?(x)}
=> ["two", "three"]



On 8/1/08, Milo Thurston <knirirr@gmail.com> wrote:
> Using irb I set up the following arrays:
>
>>> arr1
> => ["one", "two", "three"]
>>> arr2
> => ["two", "three", "four"]
>
> I would expect to be able to collect the elements of arr1 that are also
> in arr2 using select and grep, i.e.
>
>>> arr1.select { |y| arr2.grep(y) }
> => ["two", "three"]
>
> But what I actually get is:
>
>>> arr1.select { |y| arr2.grep(y) }
> => ["one", "two", "three"]
>
> What is my error or misunderstanding here?
>
> Before anyone asks, I'm not using  the array intersecttion (arr1 & arr2)
> because I am testing this expression prior to using it to find objects
> in an array (arr1) where an object parameter is found in an array of
> strings (arr2), e.g. to find all people from the array of people objects
> whose first name is in a list of names:
>
> arr1.select { |y| arr2.grep(y.string_of_interest) }
>
> Although if there's a better way of doing that I'd be interested to
> know.
> --
> Posted via http://www.ruby-forum.com/.
>
>


-- 
Me, I imagine places that I have never seen / The colored lights in
fountains, blue and green / And I imagine places that I will never go
/ Behind these clouds that hang here dark and low
But it's there when I'm holding you / There when I'm sleeping too /
There when there's nothing left of me / Hanging out behind the
burned-out factories / Out of reach but leading me / Into the
beautiful sea