Hi This part of the description of task is unclear "first line of each of the five groups". To what 5 groups do you refer ? Simply after putting the lines in a file called dat.txt get started by pulling the columns using auto split switch -a. 
perl -ane '{print $F[5]," ",$F[6],"\n";}' < dat.txt
-135.185 178.150
-49.668 -31.158
... snip
-81.417 52.986
-83.126 -56.051

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Now do a simple ave 
perl -ane '{$t5+=$F[5]; $t6+=$F[6]; $t+=1}
         END{print $t5/$t," ",$t6/$t,"\n";}' < dat.txt

-85.6206666666667 30.2721333333333

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Just guessing what is meant by "5 groups". This example uses the contents of Field 3 ( counting from 0 ) to do the grouping 
 perl -ane '{$t5{$F[3]}+=$F[5]; $t6{$F[3]}+=$F[6]; $t{$F[3]}+=1} 
                  END{foreach $i (keys %t5) 
                          {print "Group $i ",$t5{$i}/$t{$i}," ",$t6{$i
+}/$t{$i},"\n";}}  ' < dat.txt
Group S -75.969 10.2868
Group G -108.8372 73.3412
Group M -72.0558 7.1884

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In reply to Re: averaging a group of lines with numeric value in a text file by gannett
in thread averaging a group of lines with numeric value in a text file by Anas

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