Print out hotspots from some kind of data file

find_hotspots.rb

#!/usr/bin/env ruby

# from the command line run:
# ruby ./find_hotspots.rb FILE_NAME THRESHOLD

class Array
  def to_ranges
    compact.sort.uniq.inject([]) do |r,x|
      r.empty? || r.last.last.succ != x ? r << (x..x) : r[0..-2] << (r.last.first..x)
    end
  end
end

# read arguments from the command line
data_file = ARGV[0]
threshold = ARGV[1].to_i

# initiate a dictionary
aggregations = {}

# go through line of the file and provide the line number
File.readlines(data_file).each_with_index do |line, row_number|
  next if row_number == 0 # skip the first row
  
  # split the string, by spaces, into an array
  columns = line.split /\s+/

  # create a dictionary entry and add the 6th column's value to it
  aggregations[row_number] = columns[5]
end

# get line numbers and their aggregation column
grouped = aggregations.group_by do |line_number, aggr_value|
  aggr_value.to_f > threshold
end

# Grab just the line numbers from an array that looks like [[ROW, aggr], ...] == [ROW, ...]
hotspots = grouped[true].map do |group|
  group[0]
end

puts hotspots.to_ranges