Converting a PySpark DataFrame Column to a Python List
Last Updated :
01 Dec, 2021
In this article, we will discuss how to convert Pyspark dataframe column to a Python list.
Creating dataframe for demonstration:
Python3
import pyspark
from pyspark.sql import SparkSession
spark = SparkSession.builder.appName('sparkdf').getOrCreate()
data = [["1", "sravan", "vignan", 67, 89],
["2", "ojaswi", "vvit", 78, 89],
["3", "rohith", "vvit", 100, 80],
["4", "sridevi", "vignan", 78, 80],
["1", "sravan", "vignan", 89, 98],
["5", "gnanesh", "iit", 94, 98]]
columns = ['student ID', 'student NAME',
'college', 'subject1', 'subject2']
dataframe = spark.createDataFrame(data, columns)
dataframe.show()
|
Output:
Method 1: Using flatMap()
This method takes the selected column as the input which uses rdd and converts it into the list.
Syntax: dataframe.select(‘Column_Name’).rdd.flatMap(lambda x: x).collect()
where,
- dataframe is the pyspark dataframe
- Column_Name is the column to be converted into the list
- flatMap() is the method available in rdd which takes a lambda expression as a parameter and converts the column into list
- collect() is used to collect the data in the columns
Example 1: Python code to convert particular column to list using flatMap
Python3
print(dataframe.select('student Name').
rdd.flatMap(lambda x: x).collect())
print(dataframe.select('student ID').
rdd.flatMap(lambda x: x).collect())
|
Output:
[‘sravan’, ‘ojaswi’, ‘rohith’, ‘sridevi’, ‘sravan’, ‘gnanesh’]
[‘1’, ‘2’, ‘3’, ‘4’, ‘1’, ‘5’]
Example 2: Convert multiple columns to list.
Python3
print(dataframe.select(['student Name',
'student Name',
'college']).
rdd.flatMap(lambda x: x).collect())
|
Output:
[‘sravan’, ‘sravan’, ‘vignan’, ‘ojaswi’, ‘ojaswi’, ‘vvit’, ‘rohith’, ‘rohith’, ‘vvit’, ‘sridevi’, ‘sridevi’, ‘vignan’, ‘sravan’, ‘sravan’, ‘vignan’, ‘gnanesh’, ‘gnanesh’, ‘iit’]
Method 2: Using map()
This function is used to map the given dataframe column to list
Syntax: dataframe.select(‘Column_Name’).rdd.map(lambda x : x[0]).collect()
where,
- dataframe is the pyspark dataframe
- Column_Name is the column to be converted into the list
- map() is the method available in rdd which takes a lambda expression as a parameter and converts the column into list
- collect() is used to collect the data in the columns
Example: Python code to convert pyspark dataframe column to list using the map function.
Python3
print(dataframe.select('student Name').
rdd.map(lambda x : x[0]).collect())
print(dataframe.select('student ID').
rdd.map(lambda x : x[0]).collect())
print(dataframe.select('college').
rdd.map(lambda x : x[0]).collect())
|
Output:
[‘sravan’, ‘ojaswi’, ‘rohith’, ‘sridevi’, ‘sravan’, ‘gnanesh’]
[‘1’, ‘2’, ‘3’, ‘4’, ‘1’, ‘5’]
[‘vignan’, ‘vvit’, ‘vvit’, ‘vignan’, ‘vignan’, ‘iit’]
Method 3: Using collect()
Collect is used to collect the data from the dataframe, we will use a comprehension data structure to get pyspark dataframe column to list with collect() method.
Syntax: [data[0] for data in dataframe.select(‘column_name’).collect()]
Where,
- dataframe is the pyspark dataframe
- data is the iterator of the dataframe column
- column_name is the column in the dataframe
Example: Python code to convert dataframe columns to list using collect() method
Python3
print([data[0] for data in dataframe.
select('college').collect()])
print([data[0] for data in dataframe.
select('student ID').collect()])
print([data[0] for data in dataframe.
select('subject1').collect()])
print([data[0] for data in dataframe.
select('subject2').collect()])
|
Output:
['vignan', 'vvit', 'vvit', 'vignan', 'vignan', 'iit']
['1', '2', '3', '4', '1', '5']
[67, 78, 100, 78, 89, 94]
[89, 89, 80, 80, 98, 98]
Method 4: Using toLocalIterator()
This method is used to iterate the column values in the dataframe, we will use a comprehension data structure to get pyspark dataframe column to list with toLocalIterator() method.
Syntax: [data[0] for data in dataframe.select(‘column_name’).toLocalIterator()]
Where,
- dataframe is the pyspark dataframe
- data is the iterator of the dataframe column
- column_name is the column in the dataframe
Example: Convert pyspark dataframe columns to list using toLocalIterator() method
Python3
print([data[0] for data in dataframe.
select('college').collect()])
print([data[0] for data in dataframe.
select('student ID').toLocalIterator()])
print([data[0] for data in dataframe.
select('subject1').toLocalIterator()])
print([data[0] for data in dataframe.
select('subject2').toLocalIterator()])
|
Output:
['vignan', 'vvit', 'vvit', 'vignan', 'vignan', 'iit']
['1', '2', '3', '4', '1', '5']
[67, 78, 100, 78, 89, 94]
[89, 89, 80, 80, 98, 98]
Method 5: Using toPandas()
Used to convert a column to dataframe, and then we can convert it into a list.
Syntax: list(dataframe.select(‘column_name’).toPandas()[‘column_name’])
Where,
- toPandas() is used to convert particular column to dataframe
- column_name is the column in the pyspark dataframe
Example: Convert pyspark dataframe columns to list using toPandas() method
Python3
print(list(dataframe.select('college').
toPandas()['college']))
print(list(dataframe.select('student NAME').
toPandas()['student NAME']))
print(list(dataframe.select('subject1').
toPandas()['subject1']))
print(list(dataframe.select('subject2').
toPandas()['subject2']))
|
Output:
[‘vignan’, ‘vvit’, ‘vvit’, ‘vignan’, ‘vignan’, ‘iit’]
[‘sravan’, ‘ojaswi’, ‘rohith’, ‘sridevi’, ‘sravan’, ‘gnanesh’]
[67, 78, 100, 78, 89, 94]
[89, 89, 80, 80, 98, 98]
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