My Secret Life as a Spaghetti Coder
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With a name like each_cons, I thought you were going to iterate through all the permutations of how I could construct a list you operated upon. For example, I thought

[1,2,3,4].each_cons do |x| # I did not notice the required argument
  puts x.inspect
end
 

would output:

[[1,2,3,4], []]
[[1,2,3], [4]]
[[1,2], [3,4]]
[[1], [2,3,4]]
[[], [1,2,3,4]]

So when I needed to find the local maxima in an image projection to algorithmically find the staves in sheet music, I found myself wanting a C-style for loop.

I didn't know you'd provide me with a wonderful sliding window!

[1,2,3,4].each_cons(2) do |x|
  puts x.inspect
end

[1, 2]
[2, 3]
[3, 4]

From now on, I'll turn to you when I need that functionality. Thanks for waiting on me, each_cons. Not everyone would be as patient as you.

Warm Regards,
Sam

PS: In case you're interested, the "cons" in "each_cons" is short for "consecutive," not "construct," as Matz informed me:

Matz says 'I am not the one who come up with the name, but I suppose cons is the short form of consecutive.'

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Comments
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Actually, isn't Enumerable#each_slice(2) a closer equivalent to the original each_pair implementation?

Posted by JayTee on Nov 09, 2012 at 06:13 PM UTC - 6 hrs

Hey JayTee,

I'm guessing you mean this: http://www.codeodor.com/index.cfm/2007/12/3/Arraye... when you're asking about "the original each_pair implemenation."

Is that right?

All three things do something different:

Let's use [1, 2, 3, 4] as an example.

#each_slice(2): will split the array on every 2nd element, so our example array would go through 2 iterations: one for [1,2] and the other for [3,4].

#each_pair will go through every combination of elements. The iterations using our example array would be:
[1, 2]
[1, 3]
[1, 4]
[2, 3]
[2, 4]
[3, 4]

Finally, #each_cons(2) will have a "sliding window" effect, yielding for each iteration:
[1, 2]
[2, 3]
[3, 4]

Posted by Sammy Larbi on Nov 10, 2012 at 12:17 PM UTC - 6 hrs

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