Concatenate array elements by groups of 3? - ruby

Question

I have this array:
strings = %w(John likes Pie Diana prefers Cupcakes)
Which will look like:
strings[0] -> "John"
strings[1] -> "likes"
strings[2] -> "Pie"
strings[3] -> "Diana"
strings[4] -> "prefers"
strings[5] -> "Cupcakes"
How can I transform it into this?
strings[0] -> "John likes Pie"
strings[1] -> "Diana prefers Cupcakes"

Answer 1

strings = strings.each_slice(3).map{|a| a.join(" ")}

Answer 2

It appears (note highlighting in question) that verbs are lowercase and everything else is uppercase. Assuming that is the case*, and that the subject ('John') and verb ('likes') are always a single word, and only the first word of the object ('Apple pie') is capitalized, this should work:
def pull_substrings(strings)
(strings.each_with_index
.select { |w,_| w[0] =~ /[a-z]/ }
.map { |_,i| i-1 } << strings.size)
.each_cons(2).map { |f,lp1| strings[f...lp1].join(' ') }
end
Let's try it:
strings = %w[John likes Hot Dogs Diana prefers Cupcakes ] +
%w[Billy-Bob devourers Hot Dogs Chips And Beer]
#=> ["John", "likes", "Hot", "Dogs",
# "Diana", "prefers", "Cupcakes",
# "Billy-Bob", "devourers", "Hot", "Dogs", "Chips", "And", "Beer"]
pull_substrings(strings)
#=> ["John likes Hot Dogs", "Diana prefers Cupcakes",
# "Billy-Bob devourers Hot Dogs Chips And Beer"]
Here's what's going on with the above array strings:
# Save each word with its index
a = strings.each_with_index
#=> #<Enumerator: ...>
a.to_a #=> [["John", 0], ["likes", 1], ["Hot", 2], ["Dogs", 3],
# ["Diana", 4], ["prefers", 5], ["Cupcakes", 6],
# ["Billy-Bob", 7], ["devourers", 8], ["Hot", 9], ["Dogs", 10],
# ["Chips", 11], ["And", 12], ["Beer", 13]]
# Locate the positions of the verbs
b = a.select { |w,_| w[0] =~ /[a-z]/ }
#=> [["likes", 1], ["prefers", 5], ["devourers", 8]]
# Convert to the locations of the subjects (offsets where strings begin)
c = b.map { |_,i| i-1 }
#=> [0, 4, 7]
# Add the position of the last word of the last substring plus 1
d = c << strings.size
#=> [0, 4, 7, 14]
# Look at each pair of subject offsets
e = (d).each_cons(2)
#=> #<Enumerator: ...>
e.to_a #=> [[0, 4], [4, 7], [7, 14]]
# Map each pair of offsets to a substring
e.map { |f,lp1| strings[f...lp1].join(' ') }
#=> ["John likes Hot Dogs",
# "Diana prefers Cupcakes",
# "Billy-Bob devourers Hot Dogs Chips And Beer"]
The first element of e passed to the block following map is `[0, 4], sof => 0, lp1 => 4` and
strings[0...4].join(' ') => ["John", "likes", "Hot", "Dogs"] => "John likes Hot Dogs"
I initially tried converting strings to a string, words separated with a space, and attempted to use a regex, but that was problematic.
Pun unintended