Oops! I tested your code by reading the data from a text file to build @data, and it worked fine. While trying to
run your code with the rest of my code( I have built @data by parsing an XML file using XML::XPath), I'm getting errors similar to this

Operation `/': no method found,
    left argument in overloaded package  
        XML::XPath::Literal,right argument has no 
      overloaded magic at C:\..\xmlrecord_parse.pl line 608.

Tool completed with exit code 255
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So I've changed this portion of code, but I'm not sure if this is correct :

          return 5 if (int($_[0]) >= 40);
          return 0 if (int($_[0]) < 20);
          return ((int($_[0]) / 5) - 3);
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However, the results printed now are:

1-1-2004    5-1-2004    mild
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Whereas they should be:

1-1-2004    5-1-2004    mild
10-1-2004    14-1-2004    very warm
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Data

1-1-2004 15.0 
2-1-2004 15.5 
3-1-2004 16.5
4-1-2004 17.0
5-1-2004 17.5
6-1-2004 18.0
7-1-2004 18.5
8-1-2004 19.0
9-1-2004 19.5
10-1-2004 25.0
11-1-2004 26.5
12-1-2004 27.5
13-1-2004 28.0
14-1-2004 29.5
15-1-2004 28.0
16-1-2004 28.8
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What do I need to change in the code?
Thanks,
perl_seeker :)