Is there anything like Array#Index that takes a block?

Ruby
1

I would like to avoid doing :
Array.index(Enumerable.find { |blarg| blarg =~ /blah/ })

as that traverses the array twice. Is there any built in method that
does this for me? That is, it’s a method that takes a block and returns
the index of the first element for which this block returns true?

Thanks

2

Lee G. schrieb:

I would like to avoid doing :
Array.index(Enumerable.find { |blarg| blarg =~ /blah/ })

as that traverses the array twice. Is there any built in method that
does this for me? That is, it’s a method that takes a block and returns
the index of the first element for which this block returns true?

Thanks
yes… it’s called Array#index scnr
ri says:
array.index(obj) -> int or nil
array.index {|item| block} -> int or nil
…
If a block is given instead of an argument, returns first
object for which block is true.

so…just use #index with a blocck

3

badboy wrote:

Lee G. schrieb:

I would like to avoid doing :
Array.index(Enumerable.find { |blarg| blarg =~ /blah/ })

as that traverses the array twice. Is there any built in method that
does this for me? That is, it’s a method that takes a block and returns
the index of the first element for which this block returns true?

Thanks
yes… it’s called Array#index scnr
ri says:
array.index(obj) → int or nil
array.index {|item| block} → int or nil
…
If a block is given instead of an argument, returns first
object for which block is true.

so…just use #index with a blocck

Which version of Ruby is that for? My ri, irb and ruby don’t confirm
this. I’m using Ruby 1.8.6. Additionally RDoc Documentation
claims that Array#index only has a single implementation.

4

arr = %w{apple banana blarg blueberry}

pos = nil
arr.each_with_index do |str, i|
if str =~ /bl/
pos = i
break
end

end

puts pos

–output:–
2

5

If a block is given instead of an argument, returns first
object for which block is true.
I could not believe it says that, probably should provide a patch.

OP do not worry, of course it returns the index and not the object.
HTH
R.

6

Robert D. schrieb:

If a block is given instead of an argument, returns first
object for which block is true.
I could not believe it says that, probably should provide a patch.

OP do not worry, of course it returns the index and not the object.
HTH
R.

ah! yeah, I saw that, too but missed to mention it. It’s just a
documentation mistake

7

Lee G. schrieb:

yes… it’s called Array#index scnr
this. I’m using Ruby 1.8.6. Additionally RDoc Documentation
claims that Array#index only has a single implementation.
hm…oh =/
ruby 1.8.7 (and 1.9.1, too)

8

On Tue, Apr 28, 2009 at 4:19 PM, badboy [email protected]
wrote:

documentation mistake
yes indeed, but do you not think this is bad? I had to fire up irb to
check so have done billions of billions of Ruby users in the
universe…
Think big!
R.

9

For followers, I believe the acceptable backport for 1.8.6 is:

if RUBY_VERSION < ‘1.8.7’
class Array
alias original_index index
def index *args

 if args.length > 0
   return original_index(*args)
 else
    pos = nil
    each_with_index do |element, i|
      if yield(element)
        return i
      end
    end
   return nil
 end
end

end
end