correcting awk script to have output in correct order

Question

I have an awk "script" which sums column 3, then 4, for each value in column 1 and when column 2 > 0:

awk 'BEGIN { print "Target covered_bases percentage_covered" } {FS = "\t" } $2 > 0 { n[$1]++; covered_bases[$1] += $3 ;percentage_covered[$1] += $4 } END { for (i in n) { print i,covered_bases[i],percentage_covered[i] } }' $1

My infile would be like this:

S 0 20 0.2
S 1 300 0.7
S 2 10 0.1
D 0 10 0.3
D 1 20 0.6
D 2 2  0.02
D 3 5  0.034

And so on, to let's say Z. The output here would be:

Target covered_bases percentage_covered
S 310 0.8
D 27  0.654

So this is fine. However, the letters are output in the wrong order. I know from other questions here that awk sometimes output things not in order. My problem is I cannot seem to correct this using previous answers given in this forum as my understanding of awk is not great at all and my "script" is already quite complicated to my mind.

Could you let me know how I can correct it?

Many thanks!

Answer 1

Just pipe output of your awk to sort command but append header after awk processing.

awk '{FS = "\t" } $2 > 0 {
    n[$1]++;
    covered_bases[$1] += $3;
    percentage_covered[$1] += $4;
}
END {
    for (i in n) {
        print i,covered_bases[i],percentage_covered[i];
    }
}' $1 | sort | (echo 'Target covered_bases percentage_covered' && cat)