Compare loc[] vs iloc[] vs at[] vs iat[] with Examples


Python Pandas

In this tutorial we will discuss about loc[], iloc[], at[] and iat[] functions and their differences.

These functions are used to select one/more columns from a dataframe. They are available in the pandas  dataframe

Lets create sample dataframe

 

Create pandas DataFrame with example data

DataFrame is a data structure used to store the data in two dimensional format. It is similar to table that stores the data in rows and columns. Rows represents the records/ tuples and columns refers to the attributes.

We can create the DataFrame by using pandas.DataFrame() method.

Syntax:

pandas.DataFrame(input_data,columns,index)

Parameters:

It will take mainly three parameters

  1. input_data is represents a list of data
  2. columns represent the columns names for the data
  3. index represent the row numbers/values

We can also create a DataFrame using dictionary by skipping columns and indices.

 

Example: Python Program to create a dataframe for market data from a dictionary of food items by specifying the column names.

# import the module
import pandas

# consider the food data
food_input={'id':['foo-23','foo-13','foo-02','foo-31'],
                  'name':['ground-nut oil','almonds','flour','cereals'],
                  'cost':[567.00,562.56,67.00,76.09],
                  'quantity':[1,2,3,2]}

# pass this food to the dataframe by specifying rows 
dataframe=pandas.DataFrame(food_input,index = ['item-1', 'item-2', 'item-3', 'item-4'])

# display the dataframe
print(dataframe)

Output:

            id            name    cost  quantity
item-1  foo-23  ground-nut oil  567.00         1
item-2  foo-13         almonds  562.56         2
item-3  foo-02           flour   67.00         3
item-4  foo-31         cereals   76.09         2

You can learn more at Pandas dataframe explained with simple examples

 

Understanding the usage of loc[]

loc[] stands for location is used to select the data .

We need to specify the column names to be selected inside loc[] function.

Syntax:

dataframe.loc[:,['column',........,'column']]

where,

  1. dataframe is the input dataframe
  2. column refers to the column names
  3. : operator is used to select all rows from the column

 

Example 1: In this example, we are going to access the  name, cost and quantity columns

# import the module
import pandas

# consider the food data
food_input={'id':['foo-23','foo-13','foo-02','foo-31'],
                  'name':['ground-nut oil','almonds','flour','cereals'],
                  'cost':[567.00,562.56,67.00,76.09],
                  'quantity':[1,2,3,2]}

# pass this food to the dataframe by specifying rows 
dataframe=pandas.DataFrame(food_input,index = ['item-1', 'item-2', 'item-3', 'item-4'])

# display name ,cost and quantity columns from the dataframe
print(dataframe.loc[:,['name','cost','quantity']])

Output:

                  name    cost  quantity
item-1  ground-nut oil  567.00         1
item-2         almonds  562.56         2
item-3           flour   67.00         3
item-4         cereals   76.09         2

 

Example 2: Python program to select name and cost columns

# import the module
import pandas

# consider the food data
food_input={'id':['foo-23','foo-13','foo-02','foo-31'],
                  'name':['ground-nut oil','almonds','flour','cereals'],
                  'cost':[567.00,562.56,67.00,76.09],
                  'quantity':[1,2,3,2]}

# pass this food to the dataframe by specifying rows 
dataframe=pandas.DataFrame(food_input,index = ['item-1', 'item-2', 'item-3', 'item-4'])

# display name ,cost  columns from the dataframe
print(dataframe.loc[:,['name','cost']])

Output:

                  name    cost
item-1  ground-nut oil  567.00
item-2         almonds  562.56
item-3           flour   67.00
item-4         cereals   76.09

 

Understanding the usage of iloc[]

iloc[] stands for location is used to select the data with index .

We need to specify the column indices to be selected inside iloc[] function.

Syntax:

dataframe.loc[:,['start_column_index':'end_column_index']]

where,

  1. dataframe is the input dataframe
  2. start_column_index refers to the starting column
  3. end_column_index refers to the ending column
  4. : operator is used to select all rows from the column

 

Example 1: Python program to select name, cost and quantity columns.

# import the module
import pandas

# consider the food data
food_input={'id':['foo-23','foo-13','foo-02','foo-31'],
                  'name':['ground-nut oil','almonds','flour','cereals'],
                  'cost':[567.00,562.56,67.00,76.09],
                  'quantity':[1,2,3,2]}

# pass this food to the dataframe by specifying rows 
dataframe=pandas.DataFrame(food_input,index = ['item-1', 'item-2', 'item-3', 'item-4'])

# display name ,cost and quantity columns from the dataframe
print(dataframe.iloc[:,1:4])

Output:

                  name    cost  quantity
item-1  ground-nut oil  567.00         1
item-2         almonds  562.56         2
item-3           flour   67.00         3
item-4         cereals   76.09         2

 

Example 2: Python program to select name and cost  columns

# import the module
import pandas

# consider the food data
food_input={'id':['foo-23','foo-13','foo-02','foo-31'],
                  'name':['ground-nut oil','almonds','flour','cereals'],
                  'cost':[567.00,562.56,67.00,76.09],
                  'quantity':[1,2,3,2]}

# pass this food to the dataframe by specifying rows 
dataframe=pandas.DataFrame(food_input,index = ['item-1', 'item-2', 'item-3', 'item-4'])

# display name ,cost  columns from the dataframe
print(dataframe.iloc[:,1:3])

Output:

                  name    cost
item-1  ground-nut oil  567.00
item-2         almonds  562.56
item-3           flour   67.00
item-4         cereals   76.09

 

Understanding the usage of at[]

at[] is used to return the data in particular cell from the dataframe.

Syntax:

at[index_label,column_name]

where,

  1. dataframe is the input dataframe
  2. index_label is the index label or index position
  3. column_name is the column name

 

Example 1: Python program to get data using at[] by selecting 1 st , 2 nd and 3 rd element from name column

# import the module
import pandas

# consider the food data
food_input={'id':['foo-23','foo-13','foo-02','foo-31'],
                  'name':['ground-nut oil','almonds','flour','cereals'],
                  'cost':[567.00,562.56,67.00,76.09],
                  'quantity':[1,2,3,2]}

# pass this food to the dataframe by specifying rows 
dataframe=pandas.DataFrame(food_input,index = ['item-1', 'item-2', 'item-3', 'item-4'])

# display 1 st , 2 nd and 3 rd element from name column

print(dataframe.at['item-1','name'])
print(dataframe.at['item-2','name'])
print(dataframe.at['item-3','name'])

Output:

ground-nut oil
almonds
flour

 

Example 2: Python program to get data using at[] by selecting 1st , 2nd and 3rd element from id column

# import the module
import pandas

# consider the food data
food_input={'id':['foo-23','foo-13','foo-02','foo-31'],
                  'name':['ground-nut oil','almonds','flour','cereals'],
                  'cost':[567.00,562.56,67.00,76.09],
                  'quantity':[1,2,3,2]}

# pass this food to the dataframe by specifying rows 
dataframe=pandas.DataFrame(food_input,index = ['item-1', 'item-2', 'item-3', 'item-4'])

# display 1 st , 2 nd and 3 rd element from id column

print(dataframe.at['item-1','id'])
print(dataframe.at['item-2','id'])
print(dataframe.at['item-3','id'])

Output:

foo-23
foo-13
foo-02

 

Understanding the usage of iat[]

iat[] is used to return the data in particular cell from the dataframe based on row and column index.

Syntax:

at[row_index,column_index]

where,

  1. dataframe is the input dataframe
  2. row_index is the  index position of a row
  3. column_index is the  index position of a column

 

Example 1: Python program to get data using iat[] by selecting 1 st , 2 nd and 3 rd element from name column

# import the module
import pandas

# consider the food data
food_input={'id':['foo-23','foo-13','foo-02','foo-31'],
                  'name':['ground-nut oil','almonds','flour','cereals'],
                  'cost':[567.00,562.56,67.00,76.09],
                  'quantity':[1,2,3,2]}

# pass this food to the dataframe by specifying rows 
dataframe=pandas.DataFrame(food_input,index = ['item-1', 'item-2', 'item-3', 'item-4'])

# display 1 st , 2 nd and 3 rd element from name column

print(dataframe.iat[0,1])
print(dataframe.iat[1,1])
print(dataframe.iat[2,1])

Output:

ground-nut oil
almonds
flour

 

Example 2: Python program to get data using iat[] by selecting 1st , 2nd and 3rd element from id column

# import the module
import pandas

# consider the food data
food_input={'id':['foo-23','foo-13','foo-02','foo-31'],
                  'name':['ground-nut oil','almonds','flour','cereals'],
                  'cost':[567.00,562.56,67.00,76.09],
                  'quantity':[1,2,3,2]}

# pass this food to the dataframe by specifying rows 
dataframe=pandas.DataFrame(food_input,index = ['item-1', 'item-2', 'item-3', 'item-4'])

# display 1 st , 2 nd and 3 rd element from id column

print(dataframe.iat[0,0])
print(dataframe.iat[1,0])
print(dataframe.iat[2,0])

Output:

foo-23
foo-13
foo-02

 

Comparison between loc[] vs iloc[] vs at[] vs iat[]

  1. loc[] and iloc[] are nearly similar - loc[] will return the entire row based on row label but iloc[] will also return the entire row based on row index.
  2. at[] and iat[] are nearly similar - at[] will return the data from dataframe based on row  position/index and column name but iat[] will also return the the data from dataframe based on row  index/position and column index/position.
  3. loc[] is label based and iloc[] is position based
  4. at[] and iat[] are used to access only single element from a dataframe but loc[] and iloc[] are used to access one or more elements
  5. at[] and iat[] computation is faster than loc[] and iloc[]
  6. We can use loc[] and iloc[] to select data from one or more columns in a dataframe

 

Summary

In this article we discussed about loc[], iloc[], at[] and iat[] functions with syntax and examples. We have seen the exact differences among them using multiple examples.

 

References

 

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