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

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.