This is not a problem, but more of a question if there are other ways to do this:
I have an array:
arr = [1,2,3,4,4,5,1,4,3]
I want this output: [2,5]
My code looks like this:
arr.select { |e| arr.count(e) == 1}
Are there some alternatives to this?
Try this
arr.group_by { |e| e }.select { |k, v| v.size.eql? 1 }.keys
=> [2, 5]
collect(&:first) you could just use keys.
Your code will scan the array once per element which is acceptable for small arrays, but it should not be necessary. By looking at this blog post it is easy to come up with
arr = [1,2,3,4,4,5,1,4,3]
counts=Hash.new(0)
arr.each do |el|
counts[el]+=1
end
counts.select do |key, count|
count == 1
end.keys
which yields the same result but only traverses your array once (at the expense of two additional hashes though (which you can reduce to one by using select! if you do not need the counts :-).
One needs to have a look at the whole array first to decide the uniqueness
def one(a)
o = { }
a.each do |x|
v = o[x]
if v == nil
o[x] = true
else
if v
o[x] = false
end
end
end
return o
end
and then use this to pick the unique elements
def unique(a)
o = one(a)
b = [ ]
o.each do |k, v|
if v
b.push(k)
end
end
return b
end
Test code
a = [ 1, 2, 3, 4, 4, 5, 1, 4, 3 ]
b = unique(a)
puts "unique: #{a} -> #{b}"
Output
unique: [1, 2, 3, 4, 4, 5, 1, 4, 3] -> [2, 5]
Dedicated to Edsger W. Dijkstra
A modern, competent programmer should not be puzzle-minded, he should not revel in tricks, he should be humble and avoid clever solutions like the plague
(from EWD303)