Pig over cassandra script

data = LOAD 'cassandra://pns_fr/light_column' USING CassandraStorage();
rows  = FOREACH data GENERATE filtre.value as filtre, value_1.value as value;
filtre_on_2 = FILTER rows BY filtre==2;
group_filtre = GROUP filtre_on_2 BY filtre;
somme = FOREACH group_filtre GENERATE SUM(filtre_on_2.value);
dump somme;