perl
perl -lane '
push @{$rows{$F[0]}}, $F[1] if $. > 1
} END {
$, = " ";
print @{$rows{$_}} for (sort keys %rows);
' file
awk, assume que a entrada está ordenada na coluna 1:
awk '
NR == 1 {next}
NR == 2 {key = $1}
$1 != key {print ""; key = $1}
{printf "%s ", $2}
END {print ""}
' file