Add Enumerate A Pairing Of Every Two Sequential Items as a ruby til

README.md

@@ -9,7 +9,7 @@ and pairing with smart people at Hashrocket.
 
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-_972 TILs and counting..._
+_973 TILs and counting..._
 
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@@ -780,6 +780,7 @@ _972 TILs and counting..._
 - [Edit Previous Parts Of The Pry Buffer History](ruby/edit-previous-parts-of-the-pry-buffer-history.md)
 - [Editing Code In Pry](ruby/editing-code-in-pry.md)
 - [Encode A String As URL-Safe Base64](ruby/encode-a-string-as-url-safe-base64.md)
+- [Enumerate A Pairing Of Every Two Sequential Items](ruby/enumerate-a-pairing-of-every-two-sequential-items.md)
 - [Evaluating One-Off Commands](ruby/evaluating-one-off-commands.md)
 - [Expect A Method To Be Called And Actually Call It](ruby/expect-a-method-to-be-called-and-actually-call-it.md)
 - [FactoryGirl Sequences](ruby/factory-girl-sequences.md)

ruby/enumerate-a-pairing-of-every-two-sequential-items.md

@@ -0,0 +1,32 @@
+# Enumerate A Pairing Of Every Two Sequential Items
+
+From time to time, I've come across a situation where I want to iterate over a
+list of items and have access to the item right after (or before depending on
+how you want to think about it) the current item.
+
+If I had a list like:
+
+```ruby
+items = [:a, :b, :c, :d, :z]
+```
+
+Then I'd love to turn it into a list of tuples like so:
+
+```ruby
+tuples = [[:a, :b], [:b, :c], [:c, :d], [:d, :z]]
+```
+
+I've finally come up with a one-liner I like for turning `items` into `tuples`.
+
+```ruby
+items.first(items.size - 1)
+# => [:a, :b, :c, :d]
+items.last(items.size - 1)
+#=> [:b, :c, :d, :z]
+items.first(items.size - 1).zip(items.last(items.size - 1))
+#=> [[:a, :b], [:b, :c], [:c, :d], [:d, :z]]
+```
+
+I realized that if I take everything but the last item (using `first`) and take
+everything but the first item (using `last`), then I can `zip` those two arrays
+together into the list of tuples I was looking for.