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fix map-reduce-example formatting

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Scott R. Parish 2010-03-08 22:54:23 -06:00
parent 4e53e1b413
commit 8541b38f2b
1 changed files with 71 additions and 51 deletions
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map-reduce-example.md
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@ -10,33 +10,33 @@ This document has been shamelessly ported from the similar
Setup Setup
----- -----
To start, we’ll insert some example data which we can perform To start, we'll insert some example data which we can perform
map/reduce queries on: map/reduce queries on:
> $ ghci -package mongoDB $ ghci -package mongoDB
> GHCi, version 6.12.1: http://www.haskell.org/ghc/ :? for help GHCi, version 6.12.1: http://www.haskell.org/ghc/ :? for help
> ... ...
> Prelude> :set prompt "> " Prelude> :set prompt "> "
> > import Database.MongoDB > import Database.MongoDB
> > import Database.MongoDB.BSON > import Database.MongoDB.BSON
> > import Data.ByteString.Lazy.UTF8 > import Data.ByteString.Lazy.UTF8
> > c <- connect "localhost" [] > c <- connect "localhost" []
> > let col = (fromString "test.mr1") > let col = (fromString "test.mr1")
> > :{ > :{
> insertMany c col [ insertMany c col [
> (toBsonDoc [("x", BsonInt32 1), (toBsonDoc [("x", BsonInt32 1),
> ("tags", BsonArray [toBson "dog", ("tags", BsonArray [toBson "dog",
> toBson "cat"])]), toBson "cat"])]),
> (toBsonDoc [("x", BsonInt32 2), (toBsonDoc [("x", BsonInt32 2),
> ("tags", BsonArray [toBson "cat"])]), ("tags", BsonArray [toBson "cat"])]),
> (toBsonDoc [("x", BsonInt32 3), (toBsonDoc [("x", BsonInt32 3),
> ("tags", BsonArray [toBson "mouse", ("tags", BsonArray [toBson "mouse",
> toBson "cat", toBson "cat",
> toBson "doc"])]), toBson "doc"])]),
> (toBsonDoc [("x", BsonInt32 4), (toBsonDoc [("x", BsonInt32 4),
> ("tags", BsonArray [])]) ("tags", BsonArray [])])
> ] ]
> :} :}
Basic Map/Reduce Basic Map/Reduce
---------------- ----------------
@ -49,36 +49,43 @@ tags array, across the entire collection.
Our map function just emits a single (key, 1) pair for each tag in the Our map function just emits a single (key, 1) pair for each tag in the
array: array:
> > :{ > :{
> let mapFn = " let mapFn = "
> function() {\n function() {\n
> this.tags.forEach(function(z) {\n this.tags.forEach(function(z) {\n
> emit(z, 1);\n emit(z, 1);\n
> });\n });\n
> }" }"
> :} :}
The reduce function sums over all of the emitted values for a given The reduce function sums over all of the emitted values for a given
key: key:
> > :{ > :{
> let reduceFn = " let reduceFn = "
> function (key, values) {\n function (key, values) {\n
> var total = 0;\n var total = 0;\n
> for (var i = 0; i < values.length; i++) {\n for (var i = 0; i < values.length; i++) {\n
> total += values[i];\n total += values[i];\n
> }\n }\n
> return total;\n return total;\n
> }" }"
> :} :}
Note: We can’t just return values.length as the reduce function might Note: We can't just return values.length as the reduce function might
be called iteratively on the results of other reduce steps. be called iteratively on the results of other reduce steps.
Finally, we call map_reduce() and iterate over the result collection: Finally, we call map_reduce() and iterate over the result collection:
> > mapReduce c col (fromString mapFn) (fromString reduceFn) [] >>= allDocs > mapReduce c col (fromString mapFn) (fromString reduceFn) [] >>= allDocs
> [[(Chunk "_id" Empty,BsonString (Chunk "cat" Empty)),(Chunk "value" Empty,BsonDouble 6.0)],[(Chunk "_id" Empty,BsonString (Chunk "doc" Empty)),(Chunk "value" Empty,BsonDouble 1.0)],[(Chunk "_id" Empty,BsonString (Chunk "dog" Empty)),(Chunk "value" Empty,BsonDouble 3.0)],[(Chunk "_id" Empty,BsonString (Chunk "mouse" Empty)),(Chunk "value" Empty,BsonDouble 2.0)]] [[(Chunk "_id" Empty,BsonString (Chunk "cat" Empty)),
(Chunk "value" Empty,BsonDouble 6.0)],
[(Chunk "_id" Empty,BsonString (Chunk "doc" Empty)),
(Chunk "value" Empty,BsonDouble 1.0)],
[(Chunk "_id" Empty,BsonString (Chunk "dog" Empty)),
(Chunk "value" Empty,BsonDouble 3.0)],
[(Chunk "_id" Empty,BsonString (Chunk "mouse" Empty)),
(Chunk "value" Empty,BsonDouble 2.0)]]
Advanced Map/Reduce Advanced Map/Reduce
------------------- -------------------
@ -86,11 +93,24 @@ Advanced Map/Reduce
MongoDB returns additional information in the map/reduce results. To MongoDB returns additional information in the map/reduce results. To
obtain them, use *runMapReduce*: obtain them, use *runMapReduce*:
> > res <- runMapReduce c col (fromString mapFn) (fromString reduceFn) [] > res <- runMapReduce c col (fromString mapFn) (fromString reduceFn) []
> > res > res
> [(Chunk "result" Empty,BsonString (Chunk "tmp.mr.mapreduce_1268105512_18" Empty)),(Chunk "timeMillis" Empty,BsonInt32 90),(Chunk "counts" Empty,BsonDoc [(Chunk "input" Empty,BsonInt64 8),(Chunk "emit" Empty,BsonInt64 12),(Chunk "output" Empty,BsonInt64 4)]),(Chunk "ok" Empty,BsonDouble 1.0)] [(Chunk "result" Empty, BsonString (Chunk "tmp.mr.mapreduce_1268105512_18" Empty)),
(Chunk "timeMillis" Empty, BsonInt32 90),
(Chunk "counts" Empty,
BsonDoc [(Chunk "input" Empty,BsonInt64 8),
(Chunk "emit" Empty,BsonInt64 12),
(Chunk "output" Empty,BsonInt64 4)]),
(Chunk "ok" Empty,BsonDouble 1.0)]
You can then obtain the results using *mapReduceResults*: You can then obtain the results using *mapReduceResults*:
> > mapReduceResults c (fromString "test") res >>= allDocs > mapReduceResults c (fromString "test") res >>= allDocs
> [[(Chunk "_id" Empty,BsonString (Chunk "cat" Empty)),(Chunk "value" Empty,BsonDouble 6.0)],[(Chunk "_id" Empty,BsonString (Chunk "doc" Empty)),(Chunk "value" Empty,BsonDouble 1.0)],[(Chunk "_id" Empty,BsonString (Chunk "dog" Empty)),(Chunk "value" Empty,BsonDouble 3.0)],[(Chunk "_id" Empty,BsonString (Chunk "mouse" Empty)),(Chunk "value" Empty,BsonDouble 2.0)]] [[(Chunk "_id" Empty,BsonString (Chunk "cat" Empty)),
(Chunk "value" Empty,BsonDouble 6.0)],
[(Chunk "_id" Empty,BsonString (Chunk "doc" Empty)),
(Chunk "value" Empty,BsonDouble 1.0)],
[(Chunk "_id" Empty,BsonString (Chunk "dog" Empty)),
(Chunk "value" Empty,BsonDouble 3.0)],
[(Chunk "_id" Empty,BsonString (Chunk "mouse" Empty)),
(Chunk "value" Empty,BsonDouble 2.0)]]