Question 1: Find the number of people who are male

[
	{
		$match:{
			 gender :"male"
		}
	},
	{
		$count:"Count"
	}
]

Q2: Group authors by eye color and count the number of authors in each eye color group.

[
  {
    $group: {
      _id: "$eyeColor",
			count:{
        $sum:1
      }
    }
  },{
    $sort: {
      count: 1
    }
  }
]

Q3: Find the average age of female authors.

[
  {
    $match: {
      gender: "female"
    }
  },
  {
		$group: {
		  _id: null,
			averageAge:{
				$avg: "$age"
      }
		}
  }
]

Q4:Group authors by their eye color and, for each group, find the average age of authors and the number of authors.

[
  {
    $group: {
      _id: "$eyeColor",
      count: {
        $sum: 1
      },
      avgAge:{
        $avg:"$age"
      }
      
    }
  }
]

Q5: Which country has most number of users

[
  {
    $group: {
      _id: "$company.location.country",
      count: {
        $sum: 1
      }
    }
  },
  {
    $sort: {
      count:-1
    }
  },
  {
    $limit:1
  }
]

Q6. Get the name and age with tag ‘velit’

[
  {
    $match: {
      isActive:false,
      tags:"velit"
    }
  },
  {
		$project: {
		  name:1,
      age:1
		}
  }
]

Q7: $push. Categorise user based on their favorite fruit

[
  {
    $group: {
      _id: "$favoriteFruit",
      users: {
        $push: "$name"
      }
    }
  }
]

Q8: Lookups

[
  {
    $lookup: {
      from: "authors",
      localField: "author_id",
      foreignField: "_id",
      as: "author_details"
    }
  },
  {
    $addFields: {
      author_details: {
        $arrayElemAt:["$author_details",0]
      }
    }
  }
]

Insights