Take a string that contains colon separated lval:rval pairs, produce a hash that collects the rvals for the lvals

lval_rval_collector.rb

# Take a string that contains colon separated lval:rval pairs
# Produce a hash that collects the rvals for the lvals. E.g.
#
# "Fruit:orangeSize:largeQuantity:5Fruit:Apple"
#
# when considered with the lvals of:
#
# %w(Fruit: Size: Quantity: Fresh:)
#
# results in:
#
# {"Fruit:"=>["orange","Apple"], "Size:"=>["large"], "Quantity:"=>["5"], "Fresh:"=>[]}
#

# input
string = "Fruit:orangeSize:largeQuantity:5Fruit:Apple"

# lvals
lvals = %w(Fruit: Size: Quantity: Fresh:)

# Array to hold our "progress"; will ultimately end up with all the rvals
progress = [string]

# Result hash
result = {}

lvals.each { |split|

  # reduce by the split
  progress.map!{ |item| item.split(split) }

  # we only want 'matches' - i.e. where the split result is > 1
  # > 1 because there could be multiple occurences of the lhs
  result[split] = progress.select{ |item| item.length > 1 }.map{ |item| item[1..-1] }.flatten

  # flatten progress and remove the empty strings (these are no use)
  # all other strings need to be preserved (we can't tell whether
  # we have reduced enough)
  progress.flatten!
  progress.delete_if { |item| item.empty? }

  # We need to go back over previous processed splits and reduce
  # them by the current split; this is where this becomes an n^2
  # problem...
  result.keys.each { |doner|
    result[doner].map!{ |item|
      item.split(split).first
    }
  }
}

puts result