in reply to Parse CSV lines and process for each second

here's a pseudo-code-ish description of how you might approach this: 

my $hash={};
while (have_records){
       my $time = (date_from_record) . "-" . (time_from_record);
       if ( ! defined($hash->{$time} ) {
             $hash->{$time} = {   min => SOME_VERY_LARGE_NUMBER,
                                  max => 0 
                               }
        }

        $hash->{$time}->{min} = ( (VALUE_FROM_RECORD) < $hash->{$time}
+->{min} ? 
                                  (VALUE_FROM_RECORD) : $hash->{$time}
+->{min} ) ;

        $hash->{$time}->{max} = ( (VALUE_FROM_RECORD) > $hash->{$time}
+->{max} ? 
                                  (VALUE_FROM_RECORD) : $hash->{$time}
+->{max} ) ;
}

# NOTE:  change (date_from_record), (have_records and other 
# psuedo-values to things that are reasonable.

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Peter L. Berghold -- Unix Professional
Peter -at- Berghold -dot- Net; AOL IM redcowdawg Yahoo IM: blue_cowdawg

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Re^2: Parse CSV lines and process for each second
by capriguy84 (Novice) on Sep 07, 2011 at 19:50 UTC
    I am finding hard to understand your response. The logic I am trying to apply is
    1. Parse line1, get time-date1. Push elements to array. Go to next line.
    2. Parse line2, get time-date2. Check if time-date2 == time-date1.
    2.a. YES: Then push the elements to an array
    2.b. NO: Then print values
    The hard part is to process the first line. I am trying to use if control loop.
[reply]
          I am finding hard to understand your response. The logic I am trying to apply is

      You are trying to hard to use pushes into arrays when what you really want to do is set up what I've called in the past a "keyed abacus." Use your date/time information as a key to a hash of hashes such that each element in the hash is a hash consisting of {min, max} values. Iterate through your data, create a key into your has with the date and time concatenated, if that key already exists update the min and max elements of the hash with the new values.

      Other than writing the code out for you long hand I'm not sure how much better I can explain it. 

      #!/usr/bin/perl -w 
use strict;

my $table={};
while(my $line=<DATA>){
     chop $line;
     my ($name,$date,$time,$value)=split(/[\s]+/,$line);
     my $key = $date . "-" . $time; 
     if ( ! defined($table->{$key}) { 
          $table->{$key}={ name => '', min => 99999999, max => 0 };
     } 
     $table->{$key}->{min} = $value if $value < $table->{$key}->{min}
     $table->{$key}->{max} = $value if $value > $table -> {$key}->{max
+}
}

foreach my $key (sort keys %$table){
    my ($date,$time) = split("-",$key);
    printf "Date: %s   Time: %s   max = %d  min = %d\n",$date,$time,
               $table->{$key}->{max},
               $table->{$key}->{min};
}

exit(0);

__END__
fred            9/1/2011     15:00:00   50
mary            9/1/2011     15:00:00   0
john            9/1/2011     15:00:00   16

      [download]

      You should see an output something like: 

      Date: 9/1/2011 Max: 50  Min: 0

      [download]

      By the way...this looks like the sort of assignment I would give to my students for homework when I used to teach Perl.

      Peter L. Berghold -- Unix Professional
      Peter -at- Berghold -dot- Net; AOL IM redcowdawg Yahoo IM: blue_cowdawg
[reply]
[d/l]
[select]

        Thanks for writing up the long script and giving a new idea. I kind of understand now that you are using date-time as key and checking min & max and only then feeding in to the hash.

        If I choose this route, I have to work on other columns(5 & 6) to calculate weighted mean, get first & last value of the each second. Along with that count the max occurrences of column 6. I was able to deduce all above operations using arrays and that is the reason why I was reluctant to change the scheme.

        Btw, this is not a college assignment, I am working on some finance data to plot graphs.

        Anyone else have other ideas?
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