Trouble when using match on an array - ruby

Question

What i'm trying to do is create a method that can be given an array as an argument. The array should have some numbers in it. The method will return the number of times the array includes each number inside of it. I understand that there are probably many ways to do this, but I'd appreciate it if folks could help me understand why my way is not working rather than just advising me to do something completely different.
So I start by trying this method out
def score (dice)
dice.each do |die|
x = /(die)/.match(dice.to_s).length
end
x
end
and calling it with score ([5])expecting to get an output of 1. However, I get
NoMethodError: undefined method `length' for nil:NilClass
from t2.rb:22:in `block in score'
from t2.rb:21:in `each'
from t2.rb:21:in `score'
from (irb):2
from /home/macs/.rvm/rubies/ruby-2.0.0-p247/bin/irb:13:in `<main>'
I have also tried changing the match statement slightly (getting rid of the to_s) so it is
def score (dice)
dice.each do |die|
x = /(die)/.match(dice).length
end
x
end
and calling it with score ([5]) I get
TypeError: no implicit conversion of Array into String
from t2.rb:22:in `match'
from t2.rb:22:in `block in score'
from t2.rb:21:in `each'
from t2.rb:21:in `score'
from (irb):2
from /home/macs/.rvm/rubies/ruby-2.0.0-p247/bin/irb:13:in `<main>'
Really not sure how I'm supposed to accomplish this matching.

Answer 1

In this line
/(die)/.match(dice.to_s).length
the method match returns nil if the argument you are passing doesn't match the regular expression, which leads to this error
nil.length
# => NoMethodError: undefined method `length' for nil:NilClass
The method will return the number of times the array includes each
number inside of it.
You can try this
a = [1,1,1,2,2,1,3]
a.uniq.map { |x| a.count(x) }
# => [4, 2, 1]
a.uniq.map { |x| {x => a.count(x)} }
# => [{1=>4}, {2=>2}, {3=>1}]

Answer 2

If you want to count the occurence of each elements in the array, then you can do something like this
def score (dice)
count_hash = {}
dice.uniq.each do |die|
count_hash[die] = dice.count(die)
end
count_hash
end

Answer 3

I'd appreciate it if folks could help me understand why my way is not working ...
/(die)/ creates a Regexp, a pattern that can be matched against a string. Your pattern matches and captures die.
Regexp#match returns a MatchData object if there was a match:
/(die)/.match('a string with die') #=> #<MatchData "die" 1:"die">
# here's the match: ^^^
or nil if there was no match:
/(die)/.match('a string with dice') #=> nil
You are not working with string but with an array of integers. You convert this array to a string using Array#to_s:
dice = [5]
dice.to_s #=> "[5]"
This string doesn't contain die and therefore match returns nil:
/(die)/.match("[5]") #=> nil
Calling nil.length then raises the NoMethodError.
Passing the array "as-is" doesn't work either, because match expects a string:
/(die)/.match([5]) #=> TypeError: no implicit conversion of Array into String
Using a Regexp is not going to work here, you'll have to approach this problem in another way.

Answer 4

This is probably the most rubyish way to solve the problem:
a = [1,1,1,2,2,1,3]
p Hash[a.group_by{|x|x}.map{|key, val| [key,val.size]}]
#=> {1=>4, 2=>2, 3=>1}

Answer 5

An example that might help you implement your logic
a = [2,3,2,8,3]
a.uniq.each {|i| print i, "=>", a.to_s.scan(/#{i}/).length, " times \n" } #=> this works but ugly.
a.uniq.each {|i| print i, "=>", a.count(i), " times \n" } #=> borrowed from one of the answers.
2=>2 times
3=>2 times
8=>1 times

Answer 6

You're getting errors because in both cases you are trying to match a string (5) with the wrong thing.
This tries to match die with the entire array dice converted to a string:
dice.each do |die|
x = /(die)/.match(dice.to_s).length
end
This tries to match die with the dice array itself:
dice.each do |die|
x = /(die)/.match(dice).length
end