Group CSV file by column name

csv_groupby.rb

#!/usr/bin/env ruby

require "csv"

def print_help
  puts "Usage: ruby #{File.basename(__FILE__)} <column> <filename.csv>"
  puts "Please provide a column name and a CSV filename as an argument.\n"
end

def group_csv_by_column(filename, column)
  rows = CSV.read(filename, headers: true)
  unless rows.headers.include?(column)
    puts "Error: CSV file does not contain a '#{column}' column."
    exit
  end

  grouped = rows.group_by { |row| row[column] }

  CSV.generate do |csv|
    csv << rows.headers
    grouped.each do |_, group_rows|
      group_rows.each { |row| csv << row.fields }
    end
  end
end


if ARGV.size != 2
  print_help
else
  column = ARGV[0]
  filename = ARGV[1]

  begin
    puts group_csv_by_column(filename, column)
  rescue Errno::ENOENT
    puts "Error: File '#{filename}' not found."
  rescue StandardError => e
    puts "Error reading file: #{e.message}"
  end
end