PySpark - count()

In this PySpark tutorial, we will discuss how to get total number of values from single column/ multiple columns in two ways in an PySpark DataFrame.

Introduction:

DataFrame in PySpark is an two dimensional data structure that will store data in two dimensional format. One dimension refers to a row and second dimension refers to a column, So It will store the data in rows and columns.

Let's install pyspark module before going to this. The command to install any module in python is "pip".

Syntax:

pip install module_name

Installing PySpark:

pip install pyspark

Steps to create dataframe in PySpark:

1. Import the below modules
      import pyspark
      from pyspark.sql import SparkSession

2. Create spark app named tutorialsinhand using getOrCreate() method

     Syntax: 
     spark = SparkSession.builder.appName('tutorialsinhand').getOrCreate()

3. Create list of values for dataframe

4. Pass this list to createDataFrame() method to create pyspark dataframe
    Syntax:
    spark.createDataFrame(list of values)

Method -1 : Using select() 

count() is an aggregate function used to get the total number of values from the given column in the PySpark DataFrame.

We have to import count() method from pyspark.sql.functions

from pyspark.sql.functions import count

Syntax:

dataframe.select(count("column_name"),.............)

where, column_name is the column total count  is  returned.

Example 1:

In this example, we created pyspark dataframe with 5 rows and three columns and will get the number of values  from marks column.

# import the below modules
import pyspark
from pyspark.sql import SparkSession

# create an app
spark = SparkSession.builder.appName('tutorialsinhand').getOrCreate()

#create a  list of data
values = [{'rollno': 1, 'student name': 'Gottumukkala Sravan kumar','marks': 98},

        {'rollno': 2, 'student name': 'Gottumukkala Bobby','marks': 89},

        {'rollno': 3, 'student name': 'Lavu Ojaswi','marks': 90},

        {'rollno': 4, 'student name': 'Lavu Gnanesh','marks': 78},

        {'rollno': 5, 'student name': 'Chennupati Rohith','marks': 100}]


# create the dataframe from the values
data = spark.createDataFrame(values)


#import count function
from pyspark.sql.functions import count

#display count of  marks
print(data.select(count("marks")).collect())

Output:

We are collecting the output with collect() method.

[Row(count(marks)=5)]

Example 2:

In this example, we created pyspark dataframe with 5 rows and three columns and will get the total count  from  marks  and  rollno column.

# import the below modules
import pyspark
from pyspark.sql import SparkSession

# create an app
spark = SparkSession.builder.appName('tutorialsinhand').getOrCreate()

#create a  list of data
values = [{'rollno': 1, 'student name': 'Gottumukkala Sravan kumar','marks': 98},

        {'rollno': 2, 'student name': 'Gottumukkala Bobby','marks': 89},

        {'rollno': 3, 'student name': 'Lavu Ojaswi','marks': 90},

        {'rollno': 4, 'student name': 'Lavu Gnanesh','marks': 78},

        {'rollno': 5, 'student name': 'Chennupati Rohith','marks': 100}]


# create the dataframe from the values
data = spark.createDataFrame(values)


#import count function
from pyspark.sql.functions import count

#display count of  marks, rollno
print(data.select(count("marks"),count("rollno")).collect())

Output:

Total count of values from marks and rollno column is returned.

[Row(count(marks)=5, count(rollno)=5)]

Method -2 : Using agg() 

agg() stands for aggregation which will take dictionary in which key will be the column and value will be the count function. It will return total number of values from particular column provided as key

Syntax:

dataframe.agg({'column_name': 'count',............})

where, column_name is the column total count is  returned.

Example:

In this example, we created pyspark dataframe with 5 rows and three columns and will get the total number of values from marks  and  rollno column.

# import the below modules
import pyspark
from pyspark.sql import SparkSession

# create an app
spark = SparkSession.builder.appName('tutorialsinhand').getOrCreate()

#create a  list of data
values = [{'rollno': 1, 'student name': 'Gottumukkala Sravan kumar','marks': 98},

        {'rollno': 2, 'student name': 'Gottumukkala Bobby','marks': 89},

        {'rollno': 3, 'student name': 'Lavu Ojaswi','marks': 90},

        {'rollno': 4, 'student name': 'Lavu Gnanesh','marks': 78},

        {'rollno': 5, 'student name': 'Chennupati Rohith','marks': 100}]


# create the dataframe from the values
data = spark.createDataFrame(values)

#display total count   marks and rollno
data.agg({'marks': 'count','rollno': 'count'}).collect()

Output:

Total count  from  marks and rollno columns is returned.

[Row(count(rollno)=5, count(marks)=5)]

Gottumukkala Sravan Kumar 171FA07058
B.Tech (Hon's) - IT from Vignan's University. Published 1400+ Technical Articles on Python, R, Swift, Java, C#, LISP, PHP - MySQL and Machine Learning