Shell Programming and Scripting

a       10
a       20
a       30
b       2
b       3
b       1

a       30
b       3

awk '{a[$1]=a[$1]<$2?$2:a[$1]} END {for(i in a) print i,a[i]}'

a -1
a -2
a -3
b 1
b 2
b 3

a -3
b 3

awk '{if($2<0)a[$1]=a[$1]>$2?$2:a[$1];else a[$1]=a[$1]<$2?$2:a[$1]} END {for(i in a) print i,a[i]}'

sort -rg infile | awk '!a[$1]++'

awk '{a[$1]=sqrt($2^2)>sqrt(a[$1]^2)?$2:a[$1]}END{for(i in a) print i,a[i]}' infile

awk '$2*$2>A[$1]*A[$1]{A[$1]=$2} END{for(i in A) print i,A[i]}' infile

a -1
a -2
a -3
b 1
b 2
b 3

a -6
b 6