If you have fields in mongo which has lots duplicate values, but you want to analysis it by getting unique then you can that as I done as follows.

You can use the distinct method to retrieve unique values from a specific field in a collection. The distinct method returns an array of distinct values for a specified field across all documents in a collection.

But here we want to get unique values from multiple fields, so we can do that using $setUnion , Here is the example I worked out, hope it will be useful if someone looking for the same.

<code class="">
db.collections.aggregate([
    {
        $project: {
            fieldOne: 1,
            fieldSecond: 1
        }
    },
    {
        $group: {
            _id:null,
            fieldOnes:{$push:"$fieldOne"},
            fieldSecond:{$push:"$fieldSecond"},
        }
      },
      {
        $project:{
            fieldOnes: {$setUnion:"$fieldOnes"},
            fieldSecond: {$setUnion:"$fieldSecond"}
        }
      }
])</code>