MAPREDUCE basics

#ENCODING
import io
import sys
sys.stdout = io.TextIOWrapper(sys.stdout.buffer, encoding='utf-16')
#MONGO
from pymongo import MongoClient
client = MongoClient()
client.progzoo.authenticate('scott','tiger')
db = client['progzoo']
#PRETTY
import pprint
pp = pprint.PrettyPrinter(indent=4)

MapReduce the basics

This tutorial introduces the MapReduce command.

MapReduce examples are available.

Show a list of countries found in North America

from bson.code import Code
temp = db.world.map_reduce(
        query={"continent":"Africa"},
        map=Code("function(){emit(this.continent, this.name)}"), 
        reduce=Code("function(key, values){return values.toString()}"),
        out={"inline":1}
)

pp.pprint(
   temp["results"]
)

from bson.code import Code temp = db.world.map_reduce(query={"continent":"North America"},map=Code("function(){emit(this.continent, this.name)}"), reduce=Code("function(key, values){return values.toString()}"),out={"inline":1},) pp.pprint(temp["results"])

Show the number of countries on each continent

from bson.code import Code temp = db.world.map_reduce(

   map=Code("function(){emit(this.continent, 1)}"),
   reduce=Code("""function(key, values){
     return Array.sum(values);
   }"""),
   out={"inline":1})

pp.pprint(temp["results"])

Show the smallest 3 countries (ignore areas of 0 or None)

from bson.code import Code temp = db.world.map_reduce(

       query={"$and":[{"area":{"$ne":None}}, {"area":{"$ne":0}}]},
       sort={"area":1},
       limit=3,
       map=Code("function(){emit(this.name, this.area)}"), 
       reduce=Code("function(key, values){}"),
       out={"inline":1},

)

pp.pprint(

  temp["results"]

)

Return the first and last country based on name order for each continent

from bson.code import Code temp = db.world.map_reduce(

   map=Code("function(){emit(this.continent, {min:this.name,max:this.name})}"),
   reduce=Code("""function(key, values){
     var ret = {min:'ZZZ',max:'AAA'};
     for(var i=0;i<values.length;i++){
       if (ret.min>values[i].min) ret.min=values[i].min;
       if (ret.max<values[i].max) ret.max=values[i].max;
     }
     return ret;
   }"""),
   out={"inline":1})

pp.pprint(temp["results"])