use warnings;
use strict;

use List::Util qw(max min sum);

my %range;
while (<DATA>) {
   my ($time, $value, $error) = split /\s+/;
   push @{ $range{$time} }, $value;
}
foreach my $time (sort keys %range) {
   print "$time ";
   print min( @{ $range{$time} } ) . " ";
   print sum( @{ $range{$time} } )/@{ $range{$time} } . " ";
   print max( @{ $range{$time} } ) . "\n";
}

__DATA__
04/26/04.16:15  3.088   N
04/26/04.16:15  5.994   N
04/26/04.16:15  4.391   N
04/26/04.16:15  3.616   N
04/26/04.16:20  3.997   N
04/26/04.16:20  4.151   N
04/26/04.16:20  3.751   N
04/26/04.16:20  2.887   N
04/26/04.16:25  3.657   N
04/26/04.16:25  4.712   N
04/26/04.16:25  4.346   N
04/26/04.16:30  3.628   N
04/26/04.16:30  5.636   N
04/26/04.16:30  4.593   N
[download]

my $current_ts = '';
my $rowcount = 0;
my ($min, $max, $sum, %ec);
while (<>) {
  chomp;
  my ($ts, $v, $e) = split;
  if ($current_ts ne $ts) {
    if ($current_ts eq '') { $current_ts = $ts }
    else                   { &output_summary   }
    $current_ts = $ts;
    ($min, $max, $sum) = ($v, $v, $v);
    %ec = ($e, 1);
    $rowcount = 1;
  }
  else {
    $min = $v if ($v < $min);
    $max = $v if ($v > $max);
    $sum += $v;
    ++$rowcount;
    ++$ec{$e};
  }
}
&output_summary;

sub output_summary {
  printf "%s\t%g\t%g\t%g\t%s\n", $current_ts, $min, $max, $sum/$rowcou
+nt, join(',', keys %ec);
}
[download]

Roy Johnson,
I understand it is un-tested, so some nits:
• When you call the output_summary sub, you need to use () as a suffix or & as a prefix unless it has been previously seen.
• You forgot to chomp newlines
• ++$rowcount not +$rowcount
• ++$ec{$e} not ++%ec{$e}
• $min and $max need to have initial values prior to doing numerical comparisons
Finally, I don't think it is working correctly - shouldn't the max for :20 be 4.151?.
Here is my stab at it:

#!/usr/bin/perl
use strict;
use warnings;

my %data;
while ( <DATA> ) {
    chomp;
    my ($stamp, $reading) = split;
    next if ! $stamp || ! defined $reading;
    $data{$stamp}{COUNT}++;
    $data{$stamp}{MAX} = $reading if ! defined $data{$stamp}{MAX} || $
+reading > $data{$stamp}{MAX};
    $data{$stamp}{MIN} = $reading if ! defined $data{$stamp}{MIN} || $
+reading < $data{$stamp}{MIN};
    $data{$stamp}{SUM} += $reading;
}
print join "\t" , "TIMESTAMP", "MAX", "MIN", "AVG";
print "\n";
for my $stamp ( sort keys %data ) {
    print join "\t", $stamp, @{$data{$stamp}}{ qw(MAX MIN) }, $data{$s
+tamp}{SUM} / $data{$stamp}{COUNT};
    print "\n";
}
[download]

L~R

Based on the data you have shown. I wrote the code below. However, please be warned that I wrote this off the top of my head and it may not work or even do what I purport it to do.

use strict;
use warnings;

my @array;
my @values;
my $avg;

while(my $line = <DATA>) {
    push @array, $line;
}

foreach my $line2 (@array) {
    my ($time, $val, $err) = split / /, $line2;

    push @values, $val;

    my $tot_val += $val;

    $avg = $tot_val / $#array;
}

my @sort_max = sort {$a <=> $b} @values;
my @sort_min = soft {$b <=> $a} @values;

my $max_val = pop @sort_max;
my $min_val = pop @sort_min;

foreach my $line3 (@array) {
    my ($time, $val, $err) = split / /, $line3;

    if($val == $max_val) {
    print "max: $line3" . "\n";
    } elsif($val == $min_val) {
    print "min: $line3" . "\n";
    }
}

print "avg: $avg" . "\m";

__DATA__
04/26/04.16:15  3.088   N
04/26/04.16:15  5.994   N
04/26/04.16:15  4.391   N
04/26/04.16:15  3.616   N
04/26/04.16:20  3.997   N
04/26/04.16:20  4.151   N
04/26/04.16:20  3.751   N
04/26/04.16:20  2.887   N
04/26/04.16:25  3.657   N
04/26/04.16:25  4.712   N
04/26/04.16:25  4.346   N
04/26/04.16:30  3.628   N
04/26/04.16:30  5.636   N
04/26/04.16:30  4.593   N
[download]

        $data_min{"$timestamp"} = $seconds if (!$data_min{"$timestamp"
+});
        $data_min{"$timestamp"} = $seconds if ($seconds<$data_min{"$ti
+mestamp"});
        $data_max{"$timestamp"} = $seconds if ($seconds>$data_max{"$ti
+mestamp"});
        $data_avg{"$timestamp"}+= $seconds;
        $data_counter{"$timestamp"} ++;
[download]