Difference between revisions of "MAPREDUCE basics"
| Line 13: | Line 13: | ||
pp = pprint.PrettyPrinter(indent=4) | pp = pprint.PrettyPrinter(indent=4) | ||
</pre> | </pre> | ||
| + | |||
| + | ==MapReduce the basics== | ||
| + | <p>This tutorial introduces the <code>MapReduce</code> command.</p> | ||
| + | [[MapReduce]] examples are available. | ||
| + | <div class='extra_space' style='width:1em; height:6em;'></div> | ||
<div class=q data-lang="py3"> | <div class=q data-lang="py3"> | ||
| Line 44: | Line 49: | ||
temp = db.world.map_reduce(map=Code("function(){emit(this.continent, this.name)}"), reduce=Code("function(key, values){return values.length}"),out={"inline":1}) | temp = db.world.map_reduce(map=Code("function(){emit(this.continent, this.name)}"), reduce=Code("function(key, values){return values.length}"),out={"inline":1}) | ||
pp.pprint(temp["results"]) | pp.pprint(temp["results"]) | ||
| + | </div> | ||
| + | </div> | ||
| + | |||
| + | <div class=q data-lang="py3"> | ||
| + | <p class=strong>Show the smallest 3 countries (ignore areas of 0 or None)</p> | ||
| + | <pre class=def> | ||
| + | </pre> | ||
| + | <div class=ans> | ||
| + | from bson.code import Code | ||
| + | temp = db.world.map_reduce( | ||
| + | query={"$and":[{"area":{"$ne":None}}, {"area":{"$ne":0}}]}, | ||
| + | sort={"area":1}, | ||
| + | limit=3, | ||
| + | map=Code("function(){emit(this.name, this.area)}"), | ||
| + | reduce=Code("function(key, values){}"), | ||
| + | out={"inline":1}, | ||
| + | ) | ||
| + | |||
| + | pp.pprint( | ||
| + | temp["results"] | ||
| + | ) | ||
</div> | </div> | ||
</div> | </div> | ||
Revision as of 16:11, 29 July 2015
#ENCODING
import io
import sys
sys.stdout = io.TextIOWrapper(sys.stdout.buffer, encoding='utf-16')
#MONGO
from pymongo import MongoClient
client = MongoClient()
client.progzoo.authenticate('scott','tiger')
db = client['progzoo']
#PRETTY
import pprint
pp = pprint.PrettyPrinter(indent=4)
MapReduce the basics
This tutorial introduces the MapReduce command.
MapReduce examples are available.
Show a list of countries found in North America
from bson.code import Code
temp = db.world.map_reduce(
query={"continent":"Africa"},
map=Code("function(){emit(this.continent, this.name)}"),
reduce=Code("function(key, values){return values.toString()}"),
out={"inline":1}
)
pp.pprint(
temp["results"]
)
from bson.code import Code temp = db.world.map_reduce(query={"continent":"North America"},map=Code("function(){emit(this.continent, this.name)}"), reduce=Code("function(key, values){return values.toString()}"),out={"inline":1},) pp.pprint(temp["results"])
Show the number of countries on each continent
from bson.code import Code temp = db.world.map_reduce(map=Code("function(){emit(this.continent, this.name)}"), reduce=Code("function(key, values){return values.length}"),out={"inline":1}) pp.pprint(temp["results"])
Show the smallest 3 countries (ignore areas of 0 or None)
from bson.code import Code temp = db.world.map_reduce(
query={"$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"]
)