Subtracting numbers from adjacent columns and successive rows using awk

A solution with awk

awk '
    NR==1 {split($0,a)}
    NR==2 {split($0,b)}
    END {for(i=1;i<=NF;i++) printf "%d ", b[i]-a[i]}
' input.txt

gives a result of

0 0 8 6 4 2

Since awk interpret strings without valid numbers as 0 during arithmetic operations, in case you want to remove the results in which the source field contains non-numeric values, you can do this by adding an additional condition.

awk '
    NR==1 {split($0,a)}
    NR==2 {split($0,b)}
    END {
        for(i=1;i<=NF;i++)
        if(a[i] ~ /^[0-9]+$/ && b[i] ~ /^[0-9]+$/)
        printf "%d ", b[i]-a[i]
    }
' input.txt

gives a result of

8 6 4 2

Using awk and process input file only once:

awk 'min[$3, $5]!=""{ if(min[$3, $5]>$6){ line[$3, $5]=$0; min[$3, $5]=$6}; next }
                    { min[$3, $5]=$6; line[$3, $5]=$0 }
END{ for(x in line) print line[x] }' infile

To "keep lines with equal minimum values" in 6^th column:

awk 'min[$3, $5]!=""{ if(min[$3, $5] >$6){ line[$3, $5]=$0; min[$3, $5]=$6 };
                      if(min[$3, $5]==$6){ line[$3, $5]=line[$3, $5] ORS $0 }; next
                    }
                    { min[$3, $5]=$6; line[$3, $5]=$0 }
END{ for(x in line) print line[x] }' infile