问如何获得按键分组的平均值和标准差？

EN

> data <- read.table("foo")
> cbind(avg=with(data, tapply(V2, V1, mean)),
+       stddev=with(data, tapply(V2, V1, sd)))
  avg   stddev
0 271 169.5553
1 478 218.8630

use strict;
use warnings;
use Statistics::Descriptive;

my ($file) = @ARGV;

my @zeroes;
my @ones;

# Reading it in
open my $fh, '<', $file or die "unable to open '$file', $!";

while (my $line = <$fh>)
{
   chomp $line;
   my ($value, $number) = split("\s+", $line);
   if ($value)
   {
      push @ones, $number;
   }
   else
   {
      push @zeroes, $number;
   }
}
close $fh or warn "Can't close fh! $!";

# Stat processing
$stat_zeroes   = Statistics::Descriptive::Full->new();
$stat_ones     = Statistics::Descriptive::Full->new();

$stat_zeroes->add_data(@zeroes);
$stat_ones->add_data(@ones);

print "0: ", $stat_zeroes->mean(), " ", $stat_zeroes->standard_deviation(), "\n",
      "1: ", $stat_ones->mean(), " ", $stat_zeroes->standard_deviation(), "\n";

#!/usr/bin/perl

while (<>) {
    my ($x, $y) = split;
    $sum{$x} += $y;
    $count{$x}++;
    $sumSq{$x} += $y * $y;
}

for $i (sort keys %sum) {
    $stdev = sqrt(($sumSq{$i} - $sum{$i} * $sum{$i} / $count{$i}) / ($count{$i} - 1));
    print $i, " ", $sum{$i}/$count{$i}, " ", $stdev, "\n";
}