Need Help to make query in tMongoDbInput

[Anonymous]

Hi All,

I am executing below query in tMongoDBInput,but it gives me some error:-

"{$group : {_id : '$_wellname','$_datasetname','$_variablename', count : {$sum  : 1}}}"

Please help me to write query compatible to Mongo to get correct result,i have also attached image.

[fdenis]

give us the error