Pandas
The Pandas library is built on NumPy and provides easy-to-use data structures and data analysis tools for the Python programming language.
Use the following import convention:
>>> import pandas as pd
Pandas Data Structures
Series
A one-dimensional labeled array capable of holding any data type
>>> s = pd.Series([3, -5, 7, 4], index=['a', 'b', 'c', 'd'])
DataFrame
A two-dimensional labeled data structure with columns of potentially different types
>>> data = {'Country': ['Belgium', 'India', 'Brazil'],
'Capital': ['Brussels', 'New Delhi', 'Brasília'],
'Population': [11190846, 1303171035, 207847528]}
>>> df = pd.DataFrame(data,
columns=['Country', 'Capital', 'Population'])
I/O
Read and Write to CSV
>>> pd.read_csv('file.csv', header=None, nrows=5)
>>> df.to_csv('myDataFrame.csv')
Read and Write to Excel
>>> pd.read_excel('file.xlsx')
>>> pd.to_excel('dir/myDataFrame.xlsx', sheet_name='Sheet1')
Read multiple sheets from the same file
>>> xlsx = pd.ExcelFile('file.xls')
>>> df = pd.read_excel(xlsx, 'Sheet1')
Selection
Getting
>>> s['b'] Get one element
-5
>>> df[1:] Get subset of a DataFrame
Country Capital Population
1 India New Delhi 1303171035
2 Brazil Brasília 207847528
Selecting, Boolean Indexing & Setting
By Position
>>> df.iloc([0],[0]) Select single value by row & column
'Belgium'
>>> df.iat([0],[0])
'Belgium'
By Label
>>> df.loc([0], ['Country']) Select single value by row & column labels
'Belgium'
>>> df.at([0], ['Country'])
'Belgium'
By Label/Position
>>> df.ix[2] Select single row of
Country Brazil subset of rows
Capital Brasília
Population 207847528
>>> df.ix[:,'Capital'] Select a single column of
0 Brussels subset of columns
1 New Delhi
2 Brasília
>>> df.ix[1,'Capital'] Select rows and columns
'New Delhi'
Boolean Indexing
>>> s[~(s > 1)] Series s where value is not >1
>>> s[(s < -1) | (s > 2)] s where value is <-1 or >2
>>> df[df['Population']>1200000000] Use filter to adjust DataFrame
Setting
>>> s['a'] = 6 Set index a of Series s to 6
Read and Write to SQL Query or Database Table
>>> from sqlalchemy import create_engine
>>> engine = create_engine('sqlite:///:memory:')
>>> pd.read_sql("SELECT * FROM my_table;", engine)
>>> pd.read_sql_table('my_table', engine)
>>> pd.read_sql_query("SELECT * FROM my_table;", engine)
read_sql()is a convenience wrapper around read_sql_table() and read_sql_query()
>>> pd.to_sql('myDf', engine)
Dropping
>>> s.drop(['a', 'c']) Drop values from rows (axis=0)
>>> df.drop('Country', axis=1) Drop values from columns(axis=1
Sort & Rank
>>> df.sort_index() Sort by labels along an axis
>>> df.sort_values(by='Country') Sort by the values along an axis
>>> df.rank() Assign ranks to entries
Retrieving Series/DataFrame Information
>>> df.shape (rows,columns)
>>> df.index Describe index
>>> df.columns Describe DataFrame columns
>>> df.info() Info on DataFrame
>>> df.count() Number of non-NA values Getting Also see NumPy Arrays Selecting, Boolean Indexing & SettingBasic Information
Summary
>>> df.sum() Sum of values
>>> df.cumsum() Cummulative sum of values
>>> df.min()/df.max() Minimum/maximum values
>>> df.idxmin()/df.idxmax() Minimum/Maximum index value
>>> df.describe() Summary statistics
>>> df.mean() Mean of values
>>> df.median() Median of values
>>> f = lambda x: x*2 Applying Functions
>>> df.apply(f) Apply function
>>> df.applymap(f) Apply function element-wise
Data Alignment
Internal Data Alignment
NA values are introduced in the indices that don’t overlap:
>>> s3 = pd.Series([7, -2, 3], index=['a', 'c', 'd'])
>>> s + s3
a 10.0
b NaN
c 5.0
d 7.0
Arithmetic Operations with Fill Methods
You can also do the internal data alignment yourself with the help of the fill methods:
>>> s.add(s3, fill_value=0)
a 10.0
b -5.0
c 5.0
d 7.0
>>> s.sub(s3, fill_value=2)
>>> s.div(s3, fill_value=4)
>>> s.mul(s3, fill_value=3)
