Average of multiple files without considering missing values

Question

I want to calculate the average of 15 files:- ifile1.txt, ifile2.txt, ....., ifile15.txt. Number of columns and rows of each file are same. But some of them are missing values.

Answer 1

awk 'FNR == 1 { nfiles++; ncols = NF }
  { for (i = 1; i < NF; i++) 
        if ( $i != "?" ) { sum[FNR,i] += $i ; count[FNR,i]++ ;}
   if (FNR > maxnr) maxnr = FNR
  }
  END {
  for (line = 1; line <= maxnr; line++)
  {
     for (col = 1; col < ncols; col++)
          if ( count[line,col] > 0 ) printf "  %f", sum[line,col]/count[line,col];
          else printf " ? " ;
     printf "\n" ;
  }
}' ifile*.txt

I just check the '?' ...