Beefy Boxes and Bandwidth Generously Provided by pair Networks
The stupid question is the question not asked
 
PerlMonks  

Comment on

( #3333=superdoc: print w/ replies, xml ) Need Help??

One comment that I would make, also, (tangental to the immediate discussion though it be ...) is that unexpectedly-good results can be obtained by using “an old COBOL trick,” namely, use an external disk-sort to sort the file first.   Then, you can simply read the file sequentially.   Every occurrence of every value in every group will be adjacent ... just count ’em up until the value changes (or until end-of-file).   Any gap in the sequence indicates a complete absence of values, anywhere in the original file, that falls into that gap.   The amount of memory required is:   “basically, none.”

And, yes ... you can sort a file of millions of entries and you’ll be quite pleasantly surprised at how well even a run-of-the-mill disk sorter (or Perl module) can get the job done.   It isn’t memory intensive (although it will efficiently use what memory is available).   It is disk-space intensive, as it will create and discard many temporary spill-files, but moderately so.

The same technique is also ideally suited to comparing large files, or for merging them, because there is no “searching” to be done at all.   Merely sort all of the files the same way, and the process is once again sequential.


In reply to Re: "Just use a hash": An overworked mantra? by sundialsvc4
in thread "Just use a hash": An overworked mantra? by davido

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post; it's "PerlMonks-approved HTML":



  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • Outside of code tags, you may need to use entities for some characters:
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.
  • Log In?
    Username:
    Password:

    What's my password?
    Create A New User
    Chatterbox?
    and the web crawler heard nothing...

    How do I use this? | Other CB clients
    Other Users?
    Others cooling their heels in the Monastery: (4)
    As of 2014-10-25 03:11 GMT
    Sections?
    Information?
    Find Nodes?
    Leftovers?
      Voting Booth?

      For retirement, I am banking on:










      Results (141 votes), past polls