map and aggregate for shell

mapagg

#!/usr/bin/env ruby

# map and aggregate for shell pipelines

# Two args: mapper, then agger
#   mapper is evaluated within each line
#   agger is evaluated within an array holding all mapper results
#
# do a sum
#   cat numbers | mapagg to_i 'inject(0){|s,x| s+x}'
# find max value in column
#   cat tsv | mapagg 'split("\t")[0].to_i'  sort[0]

raise "exactly two args: mapper, then the agger.  (or leave out agger)" unless ARGV.size >= 1

# for crazy nonsense like dotfiles.org/~brendano/.irbrc
if File.exists?("#{ENV['HOME']}/.irbrc")
  $irbrc_extensions_only = true
  load "~/.irbrc"
end

cmd = ARGV[0]
mapped = STDIN.map do |line|
  line.chomp.instance_eval { eval cmd }
end

cmd = ARGV[1] || "self"
result = mapped.instance_eval { eval cmd }
puts result