Python Pandas - DataFrame

A DataFrame in Python's pandas library is a two-dimensional labeled data structure that is used for data manipulation and analysis. It can handle different data types such as integers, floats, and strings. Each column has a unique label, and each row is labeled with a unique index value, which helps in accessing specific rows.

DataFrame is used in machine learning tasks which allow the users to manipulate and analyze the data sets in large size. It supports the operations such as filtering, sorting, merging, grouping and transforming data.

Features of DataFrame

Following are the features of the Pandas DataFrame −

• Columns can be of different types.
• Size is mutable.
• Labeled axes (rows and columns).
• Can Perform Arithmetic operations on rows and columns.

Python Pandas DataFrame Structure

You can think of a DataFrame as similar to an SQL table or a spreadsheet data representation. Let us assume that we are creating a data frame with student's data.

Creating a pandas DataFrame

A pandas DataFrame can be created using the following constructor −

pandas.DataFrame(data=None, index=None, columns=None, dtype=None, copy=None)

The parameters of the constructor are as follows −

Creating a DataFrame from Different Inputs

A pandas DataFrame can be created using various inputs like −

• Lists
• Dictionary
• Series
• Numpy ndarrays
• Another DataFrame
• External input iles like CSV, JSON, HTML, Excel sheet, and more.

In the subsequent sections of this chapter, we will see how to create a DataFrame using these inputs.

Create an Empty DataFrame

An empty DataFrame can be created using the DataFrame constructor without any input.

Example

Following is the example creating an empty DataFrame.

#import the pandas library and aliasing as pdimport pandas as pddf = pd.DataFrame()print(df)

Itsoutput is as follows −

Empty DataFrameColumns: []Index: []

Create a DataFrame from Lists

The DataFrame can be created using a single list or a list of lists.

Example

The following example demonstrates how to create a pandas DataFrame from a Python list object.

import pandas as pddata = [1,2,3,4,5]df = pd.DataFrame(data)print(df)

Itsoutput is as follows −

     00    11    22    33    44    5

Example

Here is another example of creating a Pandas DataFrame from the Python list of list.

import pandas as pddata = [['Alex',10],['Bob',12],['Clarke',13]]df = pd.DataFrame(data,columns=['Name','Age'])print(df)

Itsoutput is as follows −

      Name      Age0     Alex      101     Bob       122     Clarke    13

Create a DataFrame from Dict of ndarrays / Lists

All thendarrays must be of same length. If index is passed, then the length of the index should equal to the length of the arrays.

If no index is passed, then by default, index will be range(n), wheren is the array length.

Example

Here is the example of creating the DataFrame from a Python dictionary.

import pandas as pddata = {'Name':['Tom', 'Jack', 'Steve', 'Ricky'],'Age':[28,34,29,42]}df = pd.DataFrame(data)print(df)

Itsoutput is as follows −

      Age      Name0     28        Tom1     34       Jack2     29      Steve3     42      Ricky

Note − Observe the values 0,1,2,3. They are the default index assigned to each using the function range(n).

Example

Let us now create an indexed DataFrame using arrays.

import pandas as pddata = {'Name':['Tom', 'Jack', 'Steve', 'Ricky'],'Age':[28,34,29,42]}df = pd.DataFrame(data, index=['rank1','rank2','rank3','rank4'])print(df)

Itsoutput is as follows −

         Age    Namerank1    28      Tomrank2    34     Jackrank3    29    Steverank4    42    Ricky

Note − Observe, theindex parameter assigns an index to each row.

Create a DataFrame from List of Dicts

List of Dictionaries can be passed as input data to create a DataFrame. The dictionary keys are by default taken as column names.

Example

The following example shows how to create a DataFrame by passing a list of dictionaries.

import pandas as pddata = [{'a': 1, 'b': 2},{'a': 5, 'b': 10, 'c': 20}]df = pd.DataFrame(data)print(df)

Itsoutput is as follows −

    a    b      c0   1   2     NaN1   5   10   20.0

Note − Observe, NaN (Not a Number) is appended in missing areas.

Example

The following example shows how to create a DataFrame with a list of dictionaries, row indices, and column indices.

import pandas as pddata = [{'a': 1, 'b': 2},{'a': 5, 'b': 10, 'c': 20}]#With two column indices, values same as dictionary keysdf1 = pd.DataFrame(data, index=['first', 'second'], columns=['a', 'b'])#With two column indices with one index with other namedf2 = pd.DataFrame(data, index=['first', 'second'], columns=['a', 'b1'])print(df1)print(df2)

Itsoutput is as follows −

#df1 output         a  bfirst    1  2second   5  10#df2 output         a  b1first    1  NaNsecond   5  NaN

Note − Observe, df2 DataFrame is created with a column index other than the dictionary key; thus, appended the NaNs in place. Whereas, df1 is created with column indices same as dictionary keys, so NaNs appended.

Create a DataFrame from Dict of Series

Dictionary of Series can be passed to form a DataFrame. The resultant index is the union of all the series indexes passed.

Example

Here is the example −

import pandas as pdd = {'one' : pd.Series([1, 2, 3], index=['a', 'b', 'c']),   'two' : pd.Series([1, 2, 3, 4], index=['a', 'b', 'c', 'd'])}df = pd.DataFrame(d)print(df)

Itsoutput is as follows −

      one    twoa     1.0    1b     2.0    2c     3.0    3d     NaN    4

Note − Observe, for the series one, there is no labeld passed, but in the result, for thed label, NaN is appended with NaN.

Example

Another example of creating a Pandas DataFrame from a Series −

import pandas as pddata = pd.Series([1, 2, 3, 4], index=['a', 'b', 'c', 'd'])df = pd.DataFrame(data)print(df)

Itsoutput is as follows −

       0a      1b      2c      3d      4