Ruby array to hash with dates as keys - ruby

Question

I have an array that looks like this:
[
["20180630", "14:49", "google", "iOS", "Safari", "1"],
["20180630", "12:22", "google", "Android", "Chrome", "2"],
["20180629", "17:20", "google", "iOS", "Safari", "1"],
["20180629", "16:30", "(direct)", "iOS", "Safari", "1"],
["20180629", "09:29", "(direct)", "Android", "Chrome", "2"]
]
What I would like to have as an output is a hash where the date serves as the key:
{
"20180630": [["14:49", "google", "iOS", "Safari", "1"],["12:22", "google", "Android", "Chrome", "2"]],
"20180629": [[...],[...],[...]]
}

Answer 1

Enumerable#group_by will give you the hash-of-arrays transformation, then it's just a matter of removing the redundant column from the resulting values:
hash = input_array.group_by(&:first)
hash.each { |_, list| list.each(&:shift) }
hash
(note that modifies the original arrays; you'll need to adjust to a version with more copying and less mutation if that's a problem)

Answer 2

Here are two ways to build the desired hash. Neither mutates the given array (arr).
arr = [
["20180630", "14:49", "google", "iOS", "Safari", "1"],
["20180630", "12:22", "google", "Android", "Chrome", "2"],
["20180629", "17:20", "google", "iOS", "Safari", "1"],
["20180629", "16:30", "(direct)", "iOS", "Safari", "1"],
["20180629", "09:29", "(direct)", "Android", "Chrome", "2"]
]
arr.each_with_object({}) { |a,h| (h[a.first] ||= []) << a.drop(1) }
#=> {"20180630"=>[["14:49", "google", "iOS", "Safari", "1"],
# ["12:22", "google", "Android", "Chrome", "2"]],
# "20180629"=>[["17:20", "google", "iOS", "Safari", "1"],
# ["16:30", "(direct)", "iOS", "Safari", "1"],
# ["09:29", "(direct)", "Android", "Chrome", "2"]]}
A variant is the following.
arr.each_with_object(Hash.new { |h,k| h[k] = [] }) { |a,h| h[a.first] << a.drop(1) }
Alternatively, one can use the form of Hash#update (a.k.a merge!) that employs a block to determine the values of keys that are present in both hashes being merged.
arr.each_with_object({}) { |a,h| h.update(a.first=>[a.drop(1)]) { |_,o,n| o+n } }