如何从mongodb导入数据到熊猫？

Question 1

I have a large amount of data in a collection in mongodb which I need to analyze. How do i import that data to pandas?

I am new to pandas and numpy.

EDIT: The mongodb collection contains sensor values tagged with date and time. The sensor values are of float datatype.

Sample Data:

{
"_cls" : "SensorReport",
"_id" : ObjectId("515a963b78f6a035d9fa531b"),
"_types" : [
    "SensorReport"
],
"Readings" : [
    {
        "a" : 0.958069536790466,
        "_types" : [
            "Reading"
        ],
        "ReadingUpdatedDate" : ISODate("2013-04-02T08:26:35.297Z"),
        "b" : 6.296118156595,
        "_cls" : "Reading"
    },
    {
        "a" : 0.95574014778624,
        "_types" : [
            "Reading"
        ],
        "ReadingUpdatedDate" : ISODate("2013-04-02T08:27:09.963Z"),
        "b" : 6.29651468650064,
        "_cls" : "Reading"
    },
    {
        "a" : 0.953648289182713,
        "_types" : [
            "Reading"
        ],
        "ReadingUpdatedDate" : ISODate("2013-04-02T08:27:37.545Z"),
        "b" : 7.29679823731148,
        "_cls" : "Reading"
    },
    {
        "a" : 0.955931884300997,
        "_types" : [
            "Reading"
        ],
        "ReadingUpdatedDate" : ISODate("2013-04-02T08:28:21.369Z"),
        "b" : 6.29642922525632,
        "_cls" : "Reading"
    },
    {
        "a" : 0.95821381,
        "_types" : [
            "Reading"
        ],
        "ReadingUpdatedDate" : ISODate("2013-04-02T08:41:20.801Z"),
        "b" : 7.28956613,
        "_cls" : "Reading"
    },
    {
        "a" : 4.95821335,
        "_types" : [
            "Reading"
        ],
        "ReadingUpdatedDate" : ISODate("2013-04-02T08:41:36.931Z"),
        "b" : 6.28956574,
        "_cls" : "Reading"
    },
    {
        "a" : 9.95821341,
        "_types" : [
            "Reading"
        ],
        "ReadingUpdatedDate" : ISODate("2013-04-02T08:42:09.971Z"),
        "b" : 0.28956488,
        "_cls" : "Reading"
    },
    {
        "a" : 1.95667927,
        "_types" : [
            "Reading"
        ],
        "ReadingUpdatedDate" : ISODate("2013-04-02T08:43:55.463Z"),
        "b" : 0.29115237,
        "_cls" : "Reading"
    }
],
"latestReportTime" : ISODate("2013-04-02T08:43:55.463Z"),
"sensorName" : "56847890-0",
"reportCount" : 8
}

Question 2

pymongo might give you a hand, followings are some codes I’m using:

import pandas as pd
from pymongo import MongoClient


def _connect_mongo(host, port, username, password, db):
    """ A util for making a connection to mongo """

    if username and password:
        mongo_uri = 'mongodb://%s:%s@%s:%s/%s' % (username, password, host, port, db)
        conn = MongoClient(mongo_uri)
    else:
        conn = MongoClient(host, port)


    return conn[db]


def read_mongo(db, collection, query={}, host='localhost', port=27017, username=None, password=None, no_id=True):
    """ Read from Mongo and Store into DataFrame """

    # Connect to MongoDB
    db = _connect_mongo(host=host, port=port, username=username, password=password, db=db)

    # Make a query to the specific DB and Collection
    cursor = db[collection].find(query)

    # Expand the cursor and construct the DataFrame
    df =  pd.DataFrame(list(cursor))

    # Delete the _id
    if no_id:
        del df['_id']

    return df

Question 3

You can load your mongodb data to pandas DataFrame using this code. It works for me. Hopefully for you too.

import pymongo
import pandas as pd
from pymongo import MongoClient
client = MongoClient()
db = client.database_name
collection = db.collection_name
data = pd.DataFrame(list(collection.find()))

Question 4

Monary does exactly that, and it’s super fast. (another link)

See this cool post which includes a quick tutorial and some timings.

Question 5

As per PEP, simple is better than complicated:

import pandas as pd
df = pd.DataFrame.from_records(db.<database_name>.<collection_name>.find())

You can include conditions as you would working with regular mongoDB database or even use find_one() to get only one element from the database, etc.

and voila!

Question 6

import pandas as pd
from odo import odo

data = odo('mongodb://localhost/db::collection', pd.DataFrame)

Question 7

For dealing with out-of-core (not fitting into RAM) data efficiently (i.e. with parallel execution), you can try Python Blaze ecosystem: Blaze / Dask / Odo.

Blaze (and Odo) has out-of-the-box functions to deal with MongoDB.

A few useful articles to start off:

Introducing Blaze Expessions (with MongoDB query example)
ReproduceIt: Reddit word count
Difference between Dask Arrays and Blaze

And an article which shows what amazing things are possible with Blaze stack: Analyzing 1.7 Billion Reddit Comments with Blaze and Impala (essentially, querying 975 Gb of Reddit comments in seconds).

P.S. I’m not affiliated with any of these technologies.

Question 8

Another option I found very useful is:

from pandas.io.json import json_normalize

cursor = my_collection.find()
df = json_normalize(cursor)

this way you get the unfolding of nested mongodb documents for free.

Question 9

Using

pandas.DataFrame(list(...))

will consume a lot of memory if the iterator/generator result is large

better to generate small chunks and concat at the end

def iterator2dataframes(iterator, chunk_size: int):
  """Turn an iterator into multiple small pandas.DataFrame

  This is a balance between memory and efficiency
  """
  records = []
  frames = []
  for i, record in enumerate(iterator):
    records.append(record)
    if i % chunk_size == chunk_size - 1:
      frames.append(pd.DataFrame(records))
      records = []
  if records:
    frames.append(pd.DataFrame(records))
  return pd.concat(frames)

Question 10

http://docs.mongodb.org/manual/reference/mongoexport

export to csv and use read_csv or JSON and use DataFrame.from_records()

Question 11

Following this great answer by waitingkuo I would like to add the possibility of doing that using chunksize in line with .read_sql() and .read_csv(). I enlarge the answer from Deu Leung by avoiding go one by one each ‘record’ of the ‘iterator’ / ‘cursor’. I will borrow previous read_mongo function.

def read_mongo(db, 
           collection, query={}, 
           host='localhost', port=27017, 
           username=None, password=None,
           chunksize = 100, no_id=True):
""" Read from Mongo and Store into DataFrame """


# Connect to MongoDB
#db = _connect_mongo(host=host, port=port, username=username, password=password, db=db)
client = MongoClient(host=host, port=port)
# Make a query to the specific DB and Collection
db_aux = client[db]


# Some variables to create the chunks
skips_variable = range(0, db_aux[collection].find(query).count(), int(chunksize))
if len(skips_variable)<=1:
    skips_variable = [0,len(skips_variable)]

# Iteration to create the dataframe in chunks.
for i in range(1,len(skips_variable)):

    # Expand the cursor and construct the DataFrame
    #df_aux =pd.DataFrame(list(cursor_aux[skips_variable[i-1]:skips_variable[i]]))
    df_aux =pd.DataFrame(list(db_aux[collection].find(query)[skips_variable[i-1]:skips_variable[i]]))

    if no_id:
        del df_aux['_id']

    # Concatenate the chunks into a unique df
    if 'df' not in locals():
        df =  df_aux
    else:
        df = pd.concat([df, df_aux], ignore_index=True)

return df

Question 12

A similar approach like Rafael Valero, waitingkuo and Deu Leung using pagination:

def read_mongo(
       # db, 
       collection, query=None, 
       # host='localhost', port=27017, username=None, password=None,
       chunksize = 100, page_num=1, no_id=True):

    # Connect to MongoDB
    db = _connect_mongo(host=host, port=port, username=username, password=password, db=db)

    # Calculate number of documents to skip
    skips = chunksize * (page_num - 1)

    # Sorry, this is in spanish
    # https://www.toptal.com/python/c%C3%B3digo-buggy-python-los-10-errores-m%C3%A1s-comunes-que-cometen-los-desarrolladores-python/es
    if not query:
        query = {}

    # Make a query to the specific DB and Collection
    cursor = db[collection].find(query).skip(skips).limit(chunksize)

    # Expand the cursor and construct the DataFrame
    df =  pd.DataFrame(list(cursor))

    # Delete the _id
    if no_id:
        del df['_id']

    return df

Question 13

You can achieve what you want with pdmongo in three lines:

import pdmongo as pdm
import pandas as pd
df = pdm.read_mongo("MyCollection", [], "mongodb://localhost:27017/mydb")

If your data is very large, you can do an aggregate query first by filtering data you do not want, then map them to your desired columns.

Here is an example of mapping Readings.a to column a and filtering by reportCount column:

import pdmongo as pdm
import pandas as pd
df = pdm.read_mongo("MyCollection", [{'$match': {'reportCount': {'$gt': 6}}}, {'$unwind': '$Readings'}, {'$project': {'a': '$Readings.a'}}], "mongodb://localhost:27017/mydb")

read_mongo accepts the same arguments as pymongo aggregate

如何从mongodb导入数据到熊猫？

问题：如何从mongodb导入数据到熊猫？

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如何从mongodb导入数据到熊猫？

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