Difference between revisions of "AGGREGATE Tutorial"

Revision as of 15:42, 3 December 2015

Country Profile

For these questions you should use aggregate([]) on the collection world

Give the name and the per capita GDP for those countries with a population of at least 200 million.

per capita GDP is the GDP divided by the population.

db.world.aggregate([
    {$match:{
        population:{$gte:250000000}
    }},
    {$project:{
        _id:0,
        name:1,
        "per capita GDP": {$divide: ['$gdp',1000000]}
    }}
]).pretty()

db.world.aggregate([{"$match":{"population":{"$gte":200000000}}},{"$project":{"_id":0,"name":1,"per capita GDP": {"$divide": ["$gdp","$population"]}}}])

Give the name and the population density of all countries. Ignore results where the density is "None".

population density is the population divided by the area

Use a $match. {"area":{"$ne":0}}

db.world.aggregate([
    {$project:{
        _id:0,
        name:1,
        density: {$divide: ["$population","$area"]}
    }},
    {$match:{
        density: {$ne:null}
    }}
])

db.world.aggregate([{"$match":{"area":{"$ne":0}}},{"$project":{"_id":0,"name":1,"density":{"$divide":["$population","$area"]}}},{"$match":{"density":{"$ne":null}}}])

Show the name and population in millions for the countries of the continent South America. Divide the population by 1000000 to get population in millions.

db.world.aggregate([
    {$match:{
         
    }},
    {$project:{
        _id:0,
        name:1
    }}
])

db.world.aggregate([{"$match":{"continent":{"$eq":"South America"}}},{"$project":{"_id":0,"name":1,"population":{"$divide":["$population",1000000]}}}])

Show the name and population density for France, Germany, and Italy

db.world.aggregate([
    {$match:{
        name: {$in:['United Kingdom','United States','Brazil']},
        population: {$ne: null},
        area: {$ne: 0}
    }},
    {$project:{
        _id:0,
        name:1
    }}
])

db.world.aggregate([{"$match":{"name":{"$in":['France','Germany','Italy']},"population":{"$ne":null},"area":{"$ne":0}}},{"$project":{"_id":0,"name":1,"population density":{"$divide":["$population","$area"]}}}])

Order the continents by area from most to least.

db.world.aggregate([
    {$group:{
        _id:"$name",
        area:{$max: "$area"}
    }},
    {$sort:{
        area: -1
    }},
    {$project:{
        _id:1,
        area:1
    }}
])

   db.world.aggregate([
       {"$group":{
           "_id":"$continent",
           "area":{"$sum": "$area"}
       }},
       {"$sort":{
           "area": -1
       }},
       {"$project":{
           "_id":1,
           "area":1
       }}
   ])

Harder Questions

Print a list of names for countries in the continent of "North America" change United States to USA

db.world.aggregate([
  {$match:{
      continent:"North America"
  }},
  {$project:{
      _id:0,
      name:1
  }}
])

db.world.aggregate([{"$match":{"continent":"North America"}},{"$project":{"_id":0,"name":{"$cond": [{"$eq":["$name","United States"]},"USA","$name"]}}}])

Combine North America and South America to America, and then list the continents by area. Biggest first.

db.world.aggregate([
    {$group:{
        _id:{
            $cond: [{$eq:["$continent","North America"]},"America",
                {$cond: [{$eq:["$continent","Asia"]},"The East","$continent"]}]
        },
        area:{$sum: "$area"}
    }},
    {$sort:{
        area: -1
    }},
    {$project:{
        _id:1,
        area:1
    }}
])

db.world.aggregate([{"$group":{"_id":{"$cond":[{"$eq":["$continent","South America"]},"America",{"$cond":[{"$eq":["$continent","North America"]},"America","$continent"]}]},"area":{"$sum":"$area"}}},{"$sort":{"area":-1}},{"$project":{"_id":1,"area":1}}])

Show the name and the continent for countries beginning with N - but replace the continent Oceania with Australasia.

db.world.aggregate([
    {$match:{
        name:{$regex:"^N"}
    }},
    {$project:{
        _id:0,
        name:1
    }}
])

db.world.aggregate([{"$match":{"name":{"$regex":"^N"}}},{"$project":{"_id":0,"name":1,"continent":{"$cond":[{"$eq":["$continent","Oceania"]},"Australasia","$continent"]}}}])

Show the name and the continent but:

substitute Eurasia for Europe and Asia.
substitute America - for each country in North America or South America or Caribbean.

Only show countries beginning with A or B
If you're struggling you may want to experiment with $and,$or, etc.

db.world.aggregate([

   {$match:{
       name":{$regex:"^A|^B"}
   }},
   {$project":{
       _id:0,
       name:1,
       continent: {
           $cond: [{
               $or:[ 
                   {$eq:["$continent","Europe"]},
                   {$eq":["$continent","Asia"]}
               ]},"Eurasia",{
                   $cond: [
                       {$or:[ 
                           {$eq:["$continent","North America"]},
                           {$eq:["$continent","South America"]},
                           {$eq:["$continent","Caribbean"]}
                       ]},"America","$continent"]}
           ]}
   }}

])

Put the continents right...

    Oceania becomes Australasia
    Countries in Eurasia and Turkey go to Europe/Asia
    Caribbean islands starting with 'B' go to North America, other Caribbean islands go to South America

Show the name, the original continent and the new continent of all countries.

   db.world.aggregate([
       {"$project":{
           "_id":0,
           "name":1,
           "original": "$continent",
           "new": {
               "$cond": [
                   {"$or":[ 
                       {"$eq":["$continent","Eurasia"]},
                       {"$eq":["$name","Turkey"]}
                   ]},"Europe/Asia",{
                       "$cond":[
                           {"$eq":["$continent","Oceania"]},"Australasia",{
                               "$cond":[
                                   {"$and":[
                                       {"$eq":["$continent","Caribbean"]},
                                       {"$eq":[{"$substr":["$name",0,1]}, "B"]}
                                   ]},"North America",{
                                       "$cond":[
                                           {"$and":[
                                               {"$eq":["$continent","Caribbean"]},
                                               {"$ne":[{"$substr":["$name",0,1]}, "B"]}
                                           ]},"South America","$continent"
                                       ]
                                   }
                               ]
                           }
                       ]
                  }
               ]
           }
       }}
   ])