coaches.rb

#!/usr/bin/env ruby

require 'csv'
coach_years=CSV.read('coaches2.csv')[1..-1]

stints = coach_years.sort_by(&:reverse).each_with_object([]) do |coach_year, coach_stints|
  season, coach = coach_year
  start_year = season.split('-')[0].to_i
  end_year = start_year + 1

  last_stint = coach_stints.last
  if [coach, start_year] == last_stint&.fetch_values(:coach, :end_year)
    last_stint[:end_year] = end_year
  else
    coach_stints << { coach: coach, start_year: start_year, end_year: end_year }
  end
end

stints.sort_by!{|s| [s[:start_year], s[:end_year]]}
puts stints