Durchschnittswerte berechnen in pgfplots Diagramm

\documentclass[12pt]{article}
\usepackage[english]{babel}
\usepackage[utf8x]{inputenc}
\usepackage{amsmath}
\usepackage{tikz}
\usepackage{filecontents}
\begin{filecontents*}{input.txt}
size    none    rr  fb  wfs
0   300000  100000  100000  100000
0   400000  200000  400000  300000
0   500000  500000  500000  500000
1   605292  1521765 1629664 1750771
2   294844  1154284 1118936 1566752
3   0   0   0   0
\end{filecontents*}
\begin{filecontents*}{calc.pl}
#!/usr/bin/perl
$header = <>;
$, = ' ';
print $header;
$\ = "\n";
while (<>) {
  ($Spalte1,$Spalte2,$Spalte3,$Spalte4,$Spalte5) = split(' ', $_, -1);
  if (/^[0-9]/) {
    if ($Spalte1 ne $size && length($size) != 0) {
      print $size, $none / $n, $rr / $n, $fb / $n, $wfs / $n;
      $size = $Spalte1;
      $none = $Spalte2;
      $rr   = $Spalte3;
      $fb   = $Spalte4;
      $wfs  = $Spalte5;
      $n    = 1;
    } else {
      $size  = $Spalte1;
      $none += $Spalte2;
      $rr   += $Spalte3;
      $fb   += $Spalte4;
      $wfs  += $Spalte5;
      $n    += 1;
    }
  }
}
print $size, $none / $n, $rr / $n, $fb / $n, $wfs / $n;
\end{filecontents*}
\immediate\write18{/usr/bin/perl calc.pl input.txt > output.txt}
\usepackage{pgfplots}
\usetikzlibrary{shapes,chains,positioning,shadows}
\pgfplotsset{compat=1.7}
\usepgfplotslibrary{groupplots}
\begin{document}
\pgfplotstableread
            {output.txt}
            {\loadedtable}
\begin{figure}[!ht]
    \centering
    \begin{tikzpicture}
        \begin{axis}[ybar,%bar width=7pt,
        xlabel={UDP dtgr. size (Bytes)}, ylabel=Throughput (Mbit/s),
        grid=major,
        xtick=data,
        xticklabels = {250,500,1500,3000},
        legend columns = 1,
        legend style={legend pos=outer north east},]
        %width=0.6\textwidth,]
            \addplot table[x=size, y=none] {\loadedtable};
            \addplot table[x=size, y=rr] {\loadedtable};
            \addplot table[x=size, y=fb] {\loadedtable};
            \addplot table[x=size, y=wfs] {\loadedtable};           
            \legend{no mode,RR PS,Ext.RR PS,WFS PS} 
        \end{axis}
    \end{tikzpicture}
    \caption{Throughput results of different packet scheduling modes}
    \label{fig:m-mm-tp-comp}
 \end{figure}
\end{document}