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You basically want to calculate the intersection of two lists (and the negation of that). The following algorithm will work, assuming relatively small lists and unsorted initial input:

  1. Verify your commandline arguments (did the user specify two files, and do they exist?)
  2. Open dellist, and for each line:
    1. split/parse the line as necessary (I'm not sure what you actually want to key on... just the ID, or the whole mess?)
    2. Put the key into a %del hash, with a value of 1.
  3. Close dellist for good.
  4. Open orglist. For each line:
    1. Parse again as per 2(1), above. (Say, maybe you could write a function to re-use for that.)
    2. If the key exists in %del, you have a match; save to beepon, else save to beepoff

The more general algorithm, above, runs at near-linear time but will consume memory proportional to the number of elements in your DEL list (which is still much better than your solution, which re-reads the entire DEL list for each line of the ORG list!)

Less general option: If your initial files are known to be pre-sorted by your key value, you can traverse each with a pair of list cursors. The advantage of this approach is that it runs in strict linear time on the total number of elements across both lists, and uses a small constant amount of memory (i.e., memory does not increase with the size of the DEL list.)

You might also want to look at List::Compare (specifically, the intersection method) for a reusable solution if your data is small enough where storing both sets in RAM isn't an issue.

Have fun!

In reply to Re: Search and Remove by rjt
in thread Search and Remove by PyrexKidd

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