UNIX for Beginners Questions & Answers

"last"

awk '{if (last && $2 != last) {print last, sum; sum=0} 
sum=sum+ $3; last = $2}
 END {print last, sum}'

{
# On lines that meet condition -> if 'last' has a value and second field value of input is not equal to 'last'
if (last && $2 != last) {
        # print variables 'last' and 'sum', set 'sum' to zero
        print last, sum; sum=0
        }
# On each line 
        # define variable 'sum' with the current value of 'sum' incremented by the value third field of input
        # define variable 'last' as the value of second field.
        sum=sum+ $3; last = $2
}
END {
# print final values of 'last' and 'sum', after entire file is processed.
print last, sum
}