Write method group_by on my own [closed] - ruby

Question

Closed. This question needs details or clarity. It is not currently accepting answers.
Want to improve this question? Add details and clarify the problem by editing this post.
Closed 8 years ago.
Improve this question
I need to write the method group_by by myself. This is what I have so far:
module Enumerable
def group_by(&b)
solution = {}
self.each {|key,val|
b.call(var)
solution = { key=> (val) }
}
end
end
ary = [1,2,3,4,5,6,7,8,9,10]
p ary.group_by() { |i| i%3 }
I don't get it. I hope you can help me.

Answer 1

module Enumerable
def group_by &b; inject({}){|h, e| (h[b.call(e)] ||= []).push(e); h} end
end
[1,2,3,4,5,6,7,8,9,10].group_by{|i| i % 3}
# => {1 => [1, 4, 7, 10], 2 => [2, 5, 8], 0 => [3, 6, 9]}

Answer 2

I'm not really sure how I can help apart from post a solution, but maybe some description with what you find difficult might help?
Few issues I notice:
You are using passing two arguments into the block when the array only has 1, the value
You call the block with var which doesn't exist in the current scope, maybe you meant val?
You dont check to see if anything already exists in the new solution dictionary
You overwrite the solution dictionary every time you loop over a new value in the array
Here is what I came up with:
module Enumerable
def group_by
solution = {}
each do |value|
key = yield value
if solution.key?(key)
solution[key] << value
else
solution[key] = [value]
end
end
solution
end
end
ary = [1, 2, 3, 4, 5]
p ary.group_by { |i| i % 3 }
output:
{1=>[1, 4], 2=>[2, 5], 0=>[3]}
you might want to check if a block has been given incase someone tries to use the function wrong, consider using the statement unless block_given? but maybe you can try implement this yourself.

Answer 3

Another solution for comparison:
module Enumerable
def group_by
{}.tap do |group|
each{ |value| (group[ yield(value) ] ||= []) << value }
end
end
end
uses tap to avoid the unsightly pattern of
thing = {}
# do stuff with thing
thing # return it
uses ||= to create the new collection array of not already present
Alternatively:
module Enumerable
def group_by
Hash.new{ |h,k| h[k]=[] }.tap do |group|
each{ |value| group[ yield(value) ] << value }
group.default = nil # remove the default_proc when done
end
end
end

Answer 4

From my backports gem:
module Enumerable
def group_by
return to_enum(:group_by) unless block_given?
result = {}
each do |o|
key = yield(o)
ary = result.fetch(key){ result[key] = [] }
ary << o
end
result
end
end
Contrary to all solutions presented so far, it passes RubySpec.