Shell Programming and Scripting

cat tmp.txt
A 3
C 19
A 2
B 5
A 1
A 0
C 13
B 9
C 1

A 3
B 9
C 19

awk '{print $1}' tmp.txt | sort | uniq > grep.lst
sort -k1,1 -k2,2nr tmp.txt > tmp.sort.txt
for i in `cat grep.lst`
do
 grep $i tmp.sort.txt | head -1 >> good.out
done
cat good.out

A 3
B 9
C 19

awk '$2>M[$1]{M[$1]=$2}END{for (i in M) print i,M[i]}' file

awk '$2>M[$1]{M[$1]=$2}END{for (i in M) print i,M[i]}' file

{M[$1]=$2}

for (i in M) print i,M[i])

sort -k1,1 -k2,2nr infile | awk '!A[$1]++'