Adding similar lines in bash [duplicate] - bash

Question

This question already has answers here:
Sort keys and Sum their values in bash
(4 answers)
sum of column in text file using shell script
(4 answers)
How can I sum values in column based on the value in another column?
(5 answers)
Closed 4 years ago.
I have a file with below records:
$ cat sample.txt
ABC,100
XYZ,50
ABC,150
QWE,100
ABC,50
XYZ,100
Expecting the output to be:
$ cat output.txt
ABC,300
XYZ,150
QWE,100
I tried the below script:
PREVVAL1=0
SUM1=0
cat sam.txt | sort > /tmp/Pos.part
while read line
do
VAL1=$(echo $line | awk -F, '{print $1}')
VAL2=$(echo $line | awk -F, '{print $2}')
if [ $VAL1 == $PREVVAL1 ]
then
SUM1=` expr $SUM + $VAL2`
PREVVAL1=$VAL1
echo $VAL1 $SUM1
else
SUM1=$VAL2
PREVVAL1=$VAL1
fi
done < /tmp/Pos.part
I want to get some one liner command to get the required output. Wanted to avoid the while loop concept. I want to just add the numbers where the first column is same and show it in a single line.

Answer 1

awk -F, '{a[$1]+=$2} END{for (i in a) print i FS a[i]}' sample.txt
Output
QWE,100
XYZ,150
ABC,300
The first part is executed for each line and creates an associative array. The END part prints this array.

Answer 2

It's an awk one-liner:
awk -F, -v OFS=, '{sum[$1]+=$2} END {for (key in sum) print key, sum[key]}' sample.txt > output.txt
sum[$1] += $2 creates an associative array whose keys are the first field and values are the corresponding sums.

Answer 3

This can also be done easily enough in native bash. The following uses no external tools, no subshells and no pipelines, and is thus far faster (I'd place money on 100x the throughput on a typical/reasonable system) than your original code:
declare -A sums=( )
while IFS=, read -r name val; do
sums[$name]=$(( ${sums[$name]:-0} + val ))
done
for key in "${!sums[#]}"; do
printf '%s,%s\n' "$key" "${sums[$key]}"
done
If you want to, you can make this a one-liner:
declare -A sums=( ); while IFS=, read -r name val; do sums[$name]=$(( ${sums[$name]:-0} + val )); done; for key in "${!sums[#]}"; do printf '%s,%s\n' "$key" "${sums[$key]}"; done