map_file mapping map_file(string file) Takes a filename, reads in the file, creates and returns a mapping in the following manner: suppose the file is composed of the lines: frog This is a frog fish This is not a frog The mapping returned would have keys "frog" and "fish". map["frog"] would be "This is a frog". Also, if the data after the key in the file is numeric, it will properly convert the data to be numeric.