How do I collect and combine multiple arrays for calculation?

Question

I am collecting the values for a specific column from a named_scope as follows:

a = survey_job.survey_responses.collect(&:base_pay)

This gives me a numeric array for example (1,2,3,4,5). I can then pass this array into various functions I have created to retrieve the mean, median, standard deviation of the number set. This all works fine however I now need to start combining multiple columns of data to carry out the same types of calculation.

I need to collect the details of perhaps three fields as follows:

survey_job.survey_responses.collect(&:base_pay)
survey_job.survey_responses.collect(&:bonus_pay)
survey_job.survey_responses.collect(&:overtime_pay)

This will give me 3 arrays. I then need to combine these into a single array by adding each of the matching values together - i.e. add the first result from each array, the second result from each array and so on so I have an array of the totals.

How do I create a method which will collect all of this data together and how do I call it from the view template?

Really appreciate any help on this one...

Thanks

Simon

Answer 1

Here's a method that will combine an arbitrary number of arrays by taking the sum at each index. It'll allow each array to be of different length, too.

def combine(*arrays)
  # Get the length of the largest array, that'll be the number of iterations needed
  maxlen = arrays.map(&:length).max
  out = []

  maxlen.times do |i|
    # Push the sum of all array elements at a given index to the result array
    out.push( arrays.map{|a| a[i]}.inject(0) { |memo, value| memo += value.to_i } )
  end

  out
end

Then, in the controller, you could do

base_pay = survey_job.survey_responses.collect(&:base_pay)
bonus_pay = survey_job.survey_responses.collect(&:bonus_pay)
overtime_pay = survey_job.survey_responses.collect(&:overtime_pay)

@total_pay = combine(base_pay, bonus_pay, overtime_pay)

And then refer to @total_pay as needed in your view.

Answer 2

s = survey_job.survey_responses
pay = s.collect(&:base_pay).zip(s.collect(&:bonus_pay), s.collect(&:overtime_pay))
pay.map{|i| i.compact.inject(&:+) }

Do that, but with meaningful variable names and I think it will work.

Define a normal method in app/helpers/_helper.rb and it will work in the view

Edit: now it works if they contain nil or are of different sizes (as long as the longest array is the one on which zip is called.