CSV: Calculate totals of specific columns using awk

calc_totals.awk

# Sample usage:
# $ gawk -F, -v coli=9 -v colc=10 -f calc_totals.awk < file.csv

BEGIN{
    # Separator for the output
    sep = ","

    # coli is the position of the imps column. 
    # It is passed as an arg, eg. -v coli=9
    if (coli > 0) {
        fields["imps"] = coli
    }

    # colc is the position of the imps column. 
    # It is passed as an arg, eg. -v coli=10
    if (colc > 0) {
        fields["clicks"] = colc
    }
    
    totals["imps"] = 0
    totals["clicks"] = 0
}
{
    row = ""
    for (i = 0; i <= NF; i++){
        for (key in fields){
            if(i == fields[key]){
                if (key in totals) {
                    # Add to sum
                    totals[key] = totals[key] + $fields[key]
                }
            }
        }
    }
}
END{
    print "Impressions:", totals["imps"]
    print "Clicks:", totals["clicks"]
}