UNIX for Dummies Questions & Answers

$cat inFile
f1    f2    f3
A    7    2
B    4    2
B    2    3
C    6    5
D    15    2
D    5    3
D    10    4

$cat outFile
f1    f2    f3
A    7    2
B    3    2.5
C    6    5
D    10    3

FNR==1 {header=$0;next}
{
  cntA[$1]++
  f2[$1]+=$2
  f3[$1]+=$3
}
END {
  print header
  for(i in cntA)
    print i, f2[i]/cntA[i], f3[i]/cntA[i]
}

select f1, avg(f2), avg(f3) from $infile group by f1

(
 line # first line bypasses sort
 (
  sort 
  echo zzzEOF # add trailer to close loop
  ) | (
  zlast= zct=0 f2s=0.0 f3s=0.0
  while read f1 f2 f3
  do
   if [ "$f1" = "$zlast" -o "$f1" = "zzzEOF" ]
   then
    echo $zlast $(( $f2s/$zct )) $(( $f3s/$zct ))
    if [ "$f1" = "zzzEOF" ]
    then
     break
    fi
    zlast="$f1" zct=0 zf2s=0.0 zf3s=0.0
   fi
   (( zct++ ))
   (( zf2s += "$f2" ))
   (( zf3s += "$f3" ))
  done
  )
 ) < infile

#f1    f2    f2
a    3991037    4155442
a    3993760    4160837
a    3994154    4159990
b    308568    179762
f    3484774    3488370
f    3600005    3666058

#f1    f2    f2
a    3992980    4158760
b    308568    179762
f    3542390    3577214

FNR==1 {header=$0;next}
{
  cntA[$1]++
  f2[$1]+=$2
  f3[$1]+=$3
}
END {
  print header
  for(i in cntA)
    printf("%s%s%.0f%s%.0f\n", i, OFS,f2[i]/cntA[i], OFS, f3[i]/cntA[i])
}