Exit a block

Ruby
1

I need to step through a byte array untill I find a certain value, then
I need to check that the next item in the array is a certain value, it
is the first index that I require.

So two questions:

  1. How would you do it? (my ruby sucks, so interested in seeing decent
    code)

  2. If your in a block
    i.e.
    myarray.each_with_index{|a,i| if(a == 666):return i end}
    then how can you exit the block and return a value without continuing
    through the loop.

Thanks,
Jim.

2

On 20.02.2007 17:15, Jim B. wrote:

 i.e.
     myarray.each_with_index{|a,i| if(a == 666):return i end}

then how can you exit the block and return a value without continuing
through the loop.

You can use break or if inside a method return will work as well. I.e.
you could do

straightforward simple solution

def find_my_index(arr)
for i in 0 … arr.length-1
return i if arr[i] == 66 and arr[i+1] == 55
end

not found

nil
end

Of course there is a ton of other possible solutions… I find break
often not as useful as return because it has the drawback that
Array#each will always return the array item itself if you do not break
in between. That way you have to check the return value of #each which
I find inelegant.

Kind regards

robert

3

Thanks for your help, sometimes best just to program an old fashion for
loop :wink:

Thanks,
Jim.

4

On 2/20/07, Jim B. [email protected] wrote:

Thanks for your help, sometimes best just to program an old fashion for
loop :wink:

…except that:

for a in b
return a if a > 5
end

…is the same as:

b.each { |a| return a if a > 5 }

(Except in matters of scope.)

-austin

5

If it can be compromised to have another variable,
its more like the ruby way …

lets say myarray=[1,2,3,666,7]

myarray.each_with_index{|a,i| index = i and break if a == 666 }

index # => 3

6

On 2/20/07, Jim B. [email protected] wrote:

Thanks for your help, sometimes best just to program an old fashion for
loop :wink:

Nahh, more abstraction is a good thing =)

require 'enumerator'
class Array
  def find_my_index(x,y)
    to_enum(:each_with_index).each_cons(2) {|(a,i),(b,_)|
      return i if a == x && b == y
    }
    nil
  end
end

And then it’s just:

ary = [43,21,56,12,93,12]

puts ary.find_my_index(12,93)  # => 3
puts ary.find_my_index(93,12)  # => 4
puts ary.find_my_index(56,100) # => nil
7

Lou S. wrote:

require 'enumerator'
class Array
  def find_my_index(x,y)
    to_enum(:each_with_index).each_cons(2) {|(a,i),(b,_)|
      return i if a == x && b == y
    }
    nil
  end
end

I prefer to leave the actual searching to the Array class. Who knows, it
might cache a partial-order tree representation of the array and use
some micro-optimized search algorithm that performs O(log n) on average?

Here is a short one-line solution in that spirit:

class Array
def find_my_index x, y
i = index(x) and self[i+1] == y and i
end
end

Here is a more human readable version, if you don’t mind two extra
lines:

class Array
def find_my_index x, y
if i = index(x) and self[i+1] == y
i
end
end
end