Changes need to data array

I have a 25 mB file with 4 fields (see below) and 900,000 records. At the moment it's a tab-delimited .DAT file. I need to eliminate most of the records and to reduce the file to three fields instead of four, following some simple rules: STEP 1 - Eliminate unnecessary records 1) If Field 3 or Field 4 is blank, delete the record and look at the next record. 2) If Field 3 or Field 4 contains any alphabet letters (A-Z), delete the record and look at the next record. 3) If the value in Field 2 of the current record matches the value in Field 2 of the previous record, delete the current record (but not the previous record), then look at the next record. 4) Repeat steps 1-3 until all of the records have been examined. STEP 2 - Combine Fields 1 & 2 1) For all remaining records, combine Fields 1 and 2 into one Field, so if Field 1 contains "US" and Field 2 contains "92084" the new combined field should be: "US92084" -------------------- Here are the Fields in the original .dat file: CountryCode MailCode Longitude Latitude US 30183 34.3217 -84.562 US 30127 33.9135 US 31535 31.5046 -82.8246 The compressed file should look like this: CCMailCode Longitude Latitude US30183 34.3217 -84.562 US31535 31.5046 -82.8246 Also, I'd like to keep a copy of the program (so maybe it should be an .EXE file), because I might need to run it again in a year or so on a similar array. The program can be written in any language, I suppose. If it's in PHP, that would a bonus, so I can edit it. Thanks!