Ruby array group_by with dynamic elements

Question

array = ["a > 1 2 3", "a > 4 5 6", "a > 7 8 9", "b > 1 2 3", "b > 4 5 6", "b > 7 8 9", "b > 10 11 12"]

I'm trying to group/split an array by the beginning value of the string. I know I can use group_by if the elements are static...

array.group_by{|t| t[0]}.values

array = [["a > 1 2 3", "a > 4 5 6", "a > 7 8 9"], ["b > 1 2 3", "b > 4 5 6", "b > 7 8 9", "b > 10 11 12"]]

but anything before " > " is dynamic so I don't know how to 'match' 'a', 'b' to be bale to group them.

In future I suggest you hold off for awhile before selecting an answer. A quick selection discourages others from providing other, possibly better, answers, and imo is disrespectful to anyone still preparing an answer when the green checkmark is applied. (The second point does not apply to me, incidentally, as I began work on my answer after you had accepted an answer.) — Cary Swoveland
– Cary Swoveland, Commented Apr 10, 2014 at 15:29

xdazz · Accepted Answer · 2014-04-10 02:12:56Z

2

You could do with:

array.group_by { |t| t.split(/\s*>\s*/).first }.values

answered Apr 10, 2014 at 2:12

xdazz

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Cary Swoveland · Accepted Answer · 2014-04-10 03:11:24Z

This is another way you could do it:

Code

array.sort.chunk { |str| str[/^[a-z]+\s>/] }.map(&:last)

Explanation

array = ["a > 1 2 3", "a > 4 5 6", "a > 7 8 9", "b > 1 2 3",
         "b > 4 5 6", "b > 7 8 9", "b > 10 11 12"]
a = array.sort
  #=> ["a > 1 2 3", "a > 4 5 6", "a > 7 8 9",
  #    "b > 1 2 3", "b > 10 11 12", "b > 4 5 6", "b > 7 8 9"]
enum = a.chunk { |str| str[/^[a-z]+\s>/] }
  #=> #<Enumerator: #<Enumerator::Generator:0x0000010304ee40>:each>

To view the contents of the enumerator enum:

enum.to_a
  #=> [["a >", ["a > 1 2 3", "a > 4 5 6", "a > 7 8 9"]],
  #    ["b >", ["b > 1 2 3", "b > 10 11 12", "b > 4 5 6", "b > 7 8 9"]]]

enum.map(&:last)
  #=> [["a > 1 2 3", "a > 4 5 6", "a > 7 8 9"],
  #    ["b > 1 2 3", "b > 10 11 12", "b > 4 5 6", "b > 7 8 9"]]

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