group by 'last' value in bash

Question

I have a two-column file:

1,112
1,123
2,123
2,124
2,144
3,158
4,123
4,158
5,123

I need to know last column2 value for each column1:

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Answer 1

With GNU bash:

declare -A array   # associative array

# read from file
while IFS=, read a b; do array[$a]="$b"; done < file

# print array
for i in "${!array[@]}"; do echo "$i,${array[$i]}"; done

Output:

1,123
2,144
3,158
4,158
5,123