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// Count uniq values
pipeline = [ 
    { $group: { _id: "$internalId"}  },
    { $group: { _id: 1, count: { $sum: 1 } } }
];

//
// Run the aggregation command
//
R = db.runCommand( 
    {
    "aggregate": "logs" , 
    "pipeline": pipeline
    }
);
printjson(R);