#!/usr/bin/perl
# Fig. 5.5: fig05_05.pl
# Survey data analysis: Determining the mean, median and mode.

@opinions = ( 8, 9, 4, 7, 8, 5, 6, 4, 9, 9, 
              7, 8, 9, 5, 4, 8, 7, 8, 7, 7, 
              6, 6, 8, 9, 1, 9, 8, 7, 8, 7,
              7, 8, 9, 8, 9, 4, 9, 6, 8, 4,
              6, 7, 3, 4, 8, 7, 9, 8, 9, 2  );

# determine the mean
$total = 0;

foreach ( @opinions ) {
   $total += $_;
}

$mean = $total / @opinions;
print "Survey mean result:   $mean\n";

# determine the median
@sorted = sort { $a <=> $b } @opinions;
$middle = @sorted / 2;    # middle element subscript

# for an even number of elements, average the two middle 
# elements to determine the median; otherwise, use the 
# middle element
if ( @sorted %2 == 0 ) {  # even number of elements
   $median = 
      ( $sorted[ $middle - 1 ] + $sorted[ $middle ] ) / 2;
}
else {                    # odd number of elements
   $median = $sorted[ $middle ];
}

print "Survey median result: $median\n";

# determine the mode
$mode = 0;

foreach ( @opinions ) {
   ++$frequency[ $_ ];     # increment the frequency counter
   
   # if the current frequency is greater than the $mode's 
   # frequency, change $mode to $_
   if ( $frequency[ $_ ] > $frequency[ $mode ] ) {
      $mode = $_;
   }
}

print "Survey mode result:   $mode\n\n";

# display a frequency graph
print "Response\tFrequency\n";
print "--------\t---------\n";

foreach ( 1 .. 9 ) {
   print "$_\t\t", "*" x $frequency[ $_ ], "\n";
}


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