[ { "key" : 0 , "groups" : [ { "_id" : 4.0 , "number" : 12}]} , { "key" : 1 , "groups" : [ { "_id" : 6 , "number" : 1} , { "_id" : 1 , "number" : 1} , { "_id" : 3 , "number" : 10}]} , { "key" : 2 , "groups" : [ { "_id" : 19 , "number" : 12}]} , { "key" : 3 , "groups" : [ { "_id" : 880023 , "number" : 12}]} , { "key" : 4 , "groups" : [ { "_id" : 1 , "number" : 0} , { "_id" : 2 , "number" : 4} , { "_id" : 3 , "number" : 0} , { "_id" : 4 , "number" : 8}]} , { "key" : 5 , "groups" : [ { "_id" : 1 , "number" : 3} , { "_id" : null , "number" : 3} , { "_id" : 2 , "number" : 6}]} , { "key" : 6 , "groups" : [ { "_id" : null , "number" : 2} , { "_id" : 2 , "number" : 1} , { "_id" : 1 , "number" : 9}]} , { "key" : 7 , "groups" : [ { "_id" : 2 , "number" : 3} , { "_id" : null , "number" : 3} , { "_id" : 1 , "number" : 6}]} , { "key" : 8 , "groups" : [ { "_id" : null , "number" : 3} , { "_id" : 1 , "number" : 9}]} , { "key" : 9 , "groups" : [ { "_id" : null , "number" : 12}]} , { "key" : 10 , "groups" : [ { "_id" : null , "number" : 12}]} , { "key" : 11 , "groups" : [ { "_id" : 1 , "number" : 4} , { "_id" : null , "number" : 3} , { "_id" : 2 , "number" : 5}]} , { "key" : 12 , "groups" : [ { "_id" : null , "number" : 12}]} , { "key" : 13 , "groups" : [ { "_id" : 1 , "number" : 12}]}]