Indexing with iloc, loc and ix in pandas python

Indexing in pandas python is done mostly with the help of iloc, loc and ix. lets see an example of each .

iloc – iloc is used for indexing or selecting based on position .i.e. by row number and column number

loc – loc is used for indexing or selecting based on name .i.e. by row name and column name

ix – indexing can be done by both position and name using ix.

loc Vs iloc:

Create dataframe:

import pandas as pd
import numpy as np

#Create a DataFrame
d = {
    'Name':['Alisa','Bobby','Cathrine','Alisa','Bobby','Cathrine',
            'Alisa','Bobby','Cathrine','Alisa','Bobby','Cathrine'],
    'Exam':['Semester 1','Semester 1','Semester 1','Semester 1','Semester 1','Semester 1',
            'Semester 2','Semester 2','Semester 2','Semester 2','Semester 2','Semester 2'],
    
    'Subject':['Mathematics','Mathematics','Mathematics','Science','Science','Science',
               'Mathematics','Mathematics','Mathematics','Science','Science','Science'],
   'Score':[62,47,55,74,31,77,85,63,42,67,89,81]}

df = pd.DataFrame(d,columns=['Name','Exam','Subject','Score'])
df

so the resultant dataframe will be

Indexing with iloc:

.iloc [1:m, 1:n] – is used to select or index rows based on their position from 1 to m rows and 1 to n columns

Select row by using row number in pandas with .iloc

# select first 2 rows
df.iloc[:2]
# or
df.iloc[:2,]

output:

# select 3rd to 5th rows
df.iloc[2:5]
# or 
df.iloc[2:5,]

output:

# select all rows starting from third row
df.iloc[2:]
# or
df.iloc[2:,]

output:

Select column by using column number in pandas with .iloc

# select first 2 columns

df.iloc[:,:2]

output:

# select 1st and 4thcolumn
df.iloc[:,[0,3]]

output:

Select values by using .iloc

Select 2nd row and 3rd column value

# Select 2nd row and 3rd column value

df.iloc[1,2]

output:

‘Mathematics’

indexing with loc :

loc [[Row_names],[ column_names]] – is used to select or index rows or columns based on their name

# select row by now name

df.loc[1]

In the dataframe df has default row names from 1 to 11. So df.loc[1] denotes selecting the row by row name 1, so output will be

# select value by row label and column label using loc

df.loc[[1,2,3,4,5],['Name','Score']]

output:

Indexing with ix

Indexing with ix is the combination of indexing with iloc and loc. ix is used for indexing based on the position and as well by names.

View a column in pandas

# Get all values of column ‘Score’

df.ix[:,'Score']

Output:

View a row based on row numbers

# Get 3rd & 4th row

df.ix[4:5,]

Output:

View the value based on row and column number

df.ix[3,2]

Output:

‘Science’