Abstract: A method of comparing files takes three passes through data tables in memory to generate tables containing pointers to matches and mismatches by employing a method of keyword-index translation in which a keyword is taken from a first data table in a first pass and used as the index in loading an index table containing a pointer to the record containing that keyword. In a symmetric operation, a keyword is fetched from one table and used to interrogate the corresponding index table in a second pass. If there is a match, the record in the index table contains the pointer; and if there is a mismatch, the record contains a null. In an optional third pass, keywords are fetched from the other table and used to find records in the other table that are mismatches.