If I understand the description, you want a boolean value for each date+state tuple -- that is: "there (was | was not) at least one tornado on date X in state Y".

If that is the case, think about creating an array of 50 elements (one for each state). The value of each element is a reference to a hash, where the keys of the hash are the dates when one or more tornados occurred in the given state (the value assigned to each element is of no importance: it is the existence of a given date as a hash key for the given state that matters). So, suppose the data is like this: 

State  Date        other stuff
1      03/03/2003  one bad mother of a storm...
5      03/05/2003  nothing to write home about...
8      02/08/2003  they said it could never happen here
...

[download]
You might try something like this, just to list how many tornado days there were in each state, based on the given input report: 
my @states; # array holding one hash per state

while (<>)
{
   my ($state_number,$date) = split;
   $states[$state_number]{$date} = undef;
}

# now to summarize:
# for each state that had any tornados at all,
#    list number of tornado days:

for ( 1 .. 50 ) {
   if ( defined $states[$_] ) {
      printf( "state_id %2d: %3d tornado days\n", $_,
              scalar keys %{$states[$_]} );
   }
}

[download]
(untested, of course)

In reply to Re: Help with calculating stats from a flat-file database by graff
in thread Help with calculating stats from a flat-file database by nadocane

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!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • 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, details, 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, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            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.