BertrandBordage / django-pandas

Tools for working with pandas in your Django projects

Django Pandas

Tools for working with pandas in your Django projects

Contributors

• Christopher Clarke
• Bertrand Bordage

Dependencies

django-pandas supports Django (>=1.4.5) or later and requires django-model-utils (>= 1.4.0) and Pandas (0.12.0). Note because of problems with the requires directive of setuptools you probably need to install numpy in your virtualenv before you install this package or if you want to run the test suite

pip install numpy
python setup.py test

Some pandas functionality requires parts of the Scipy stack. You may wish to consult http://www.scipy.org/install.html for more information on installing the Scipy stack.

Contributing

Please file bugs and send pull requests to the GitHub repository and issue tracker.

Installation

Start by creating a new virtualenv for your project

mkvirtualenv myproject

Next install numpy and optionally pandas

pip install numpy
pip install pandas

You may want to consult the scipy documentation for more information on installing the Scipy stack.

Finally, install the development version of django-pandas from the github repository using pip:

pip install https://github.com/chrisdev/django-pandas/tarball/master

Usage

To use django-pandas in your Django project, modify the INSTALLED_APPS in your settings module to include django_pandas.

IO Module

The django-pandas.io module provides some convenience methods to facilitate the creation of DataFrames from Django QuerySets and saving data to the underlying models.

read_frame

Parameters

• qs: The Django QuerySet.

• fieldnames: The model field names to use in creating the frame.

  You can span a relationship in the usual Django way by using double underscores to specify a related field in another model You can span a relationship in the usual Django way by using double underscores to specify a related field in another model

• index_col: specify the field to use for the index. If the index

  field is not in the field list it will be appended

• coerce_float : boolean, default True

  Attempt to convert values to non-string, non-numeric objects (like decimal.Decimal) to floating point, useful for SQL result sets

DataFrameManager

django-pandas provides a custom manager to use with models that you want to render as Pandas Dataframes. The DataFrameManager manager provides the to_dataframe method that returns your models queryset as a Pandas DataFrame. To use the DataFrameManager, first override the default manager in your model's definition as shown in the example below

#models.py

from django_pandas.managers import DataFrameManager

class MyModel(models.Model):

    full_name = models.CharField(max_length=25)
    age = models.IntegerField()
    department = models.CharField(max_length=3)
    wage = models.FloatField()

    objects = DataFrameManager()

This will give you access to the following QuerySet methods:

• to_datafame
• to_timeseries
• to_pivot table

to_dataframe

Returns a DataFrame from the QuerySet

Parameters

• fieldnames: The model field names to utilise in creating the frame.

  to span a relationship, just use the field name of related fields across models, separated by double underscores,

• index: specify the field to use for the index. If the index

  field is not in the field list it will be appended

• fill_na: fill in missing observations using one of the following

  this is a string specifying a pandas fill method ('backfill, 'bill', 'pad', 'ffill') or a scalar value

• coerce_float: Attempt to convert the numeric non-string data

  like object, decimal etc. to float if possible

Examples

Create a dataframe using all the fields in your model as follows

qs = MyModel.objects.all()

df = qs.to_dataframe()

This will include you primary key create a DataFrame only from specified field names:

df = qs.to_dataframe(['age', 'department', 'wage'])

To set full_name as the index

qs.to_dataframe(['age', 'department', 'wage', index='full_name'])

You can use filters and excludes

qs.filter(age__gt=20, department='IT').to_dataframe(index='full_name')

to_timeseries

A convenience method for creating a time series i.e the DataFrame index is instance of a DateTime or PeriodIndex

Parameters

• fieldnames: The model field names to utilise in creating the frame.

  to span a relationship, just use the field name of related fields across models, separated by double underscores,

• index: specify the field to use for the index. If the index

  field is not in the field list it will be appended. This is mandatory.

• storage: Specify if the queryset uses the wide or long format

  for data.

• pivot_column: Required once the you specify long format

  storage. This could either be a list or string identifying the field name or combination of field. If the pivot_column is a single column then the unique values in this column become a new columns in the DataFrame If the pivot column is a list the values in these columns are concatenated (using the '-' as a separator) and these values are used for the new timeseries columns

• values: Also required if you utilize the long storage the

  values column name is use for populating new frame values

• freq: the offset string or object representing a target conversion
• rs_kwargs: Arguments based on pandas.DataFrame.resample

Examples

Using a long storage format

#models.py

class LongTimeSeries(models.Model):
    date_ix = models.DateTimeField()
    series_name = models.CharField(max_length=100)
    value = models.FloatField()

    objects = DataFrameManager()

Some sample data::

========   =====       =====
date       mame        value
========   =====       ======
2010-01-01  gdp        204699

2010-01-01  inflation  2.0

2010-01-01  wages      100.7

2010-02-01  gdp        204704

2010-02-01  inflation  2.4

2010-03-01  wages      100.4

2010-02-01  gdp        205966

2010-02-01  inflation  2.5

2010-03-01  wages      100.5
==========  ========== ======

Create a QuerySet

qs = LongTimeSeries.objects.filter(date_ix__year__gte=2010)

Create a timeseries dataframe

df = qs.to_timeseries(index='date_ix',
                      pivot_columns='series_name',
                      values='value',
                      storage='long')
df.head()

date         gdp     inflation     wages

2010-01-01   204966     2.0       100.7

2010-02-01   204704      2.4       100.4

2010-03-01   205966      2.5       100.5

Using a wide storage format

class WideTimeSeries(models.Model):
    date_ix = models.DateTimeField()
    col1 = models.FloatField()
    col2 = models.FloatField()
    col3 = models.FloatField()
    col4 = models.FloatField()

    objects = DataFrameManager()

qs = WideTimeSeries.objects.all()

rs_kwargs = {'how': 'sum', 'kind': 'period'}
df = qs.to_timeseries(index='date_ix', pivot_columns='series_name',
                      values='value', storage='long',
                      freq='M', rs_kwargs=rs_kwargs)

to_pivot_table

A convenience method for creating a pivot table from a QuerySet

Parameters

• fieldnames: The model field names to utilise in creating the frame.

  to span a relationship, just use the field name of related fields across models, separated by double underscores,

• values : column to aggregate, optional

• rows : list of column names or arrays to group on

  Keys to group on the x-axis of the pivot table

• cols : list of column names or arrays to group on

  Keys to group on the y-axis of the pivot table

• aggfunc : function, default numpy.mean, or list of functions

  If list of functions passed, the resulting pivot table will have hierarchical columns whose top level are the function names (inferred from the function objects themselves)

• fill_value : scalar, default None

  Value to replace missing values with

• margins : boolean, default False

  Add all row / columns (e.g. for subtotal / grand totals)

• dropna : boolean, default True

Example

# models.py
class PivotData(models.Model):
    row_col_a = models.CharField(max_length=15)
    row_col_b = models.CharField(max_length=15)
    row_col_c = models.CharField(max_length=15)
    value_col_d = models.FloatField()
    value_col_e = models.FloatField()
    value_col_f = models.FloatField()

    objects = DataFrameManager()

Usage

rows = ['row_col_a', 'row_col_b']
cols = ['row_col_c']

pt = qs.to_pivot_table(values='value_col_d', rows=rows, cols=cols)