
        
        
            
                
                
                    df = spark.createDataFrame([["ALEX", 20], ["BOB", 30], ["CATHY", 40]], ["name", "age"])
df.show()
                
            
            +-----+---+
| name|age|
+-----+---+
| ALEX| 20|
|  BOB| 30|
|CATHY| 40|
+-----+---+

Most methods in the PySpark SQL Functions library return Column objects whose label is governed by the method that we use. For instance, consider the lower(~) method:


        
        
            
                
                
                    df.select(F.lower("name")).show()
                
            
            +-----------+
|lower(name)|
+-----------+
|       alex|
|        bob|
|      cathy|
+-----------+

Here, the PySpark Column returned by lower(~) has the label lower(name) by default.

Assigning new label to PySpark Column using the alias method

We can assign a new label to a column by using the alias(~) method:


        
        
            
                
                
                    df.select(F.lower("name").alias("lower_name")).show()
                
            
            +----------+
|lower_name|
+----------+
|      alex|
|       bob|
|     cathy|
+----------+

Here, we have assigned the label "lower_name" to the column returned by lower(~).

Storing meta-data in PySpark Column's alias method

To store some meta-data in a PySpark Column, we can add the metadata option in alias(~):


        
        
            
                
                
                    df_new = df.select(F.lower("name").alias("lower_name", metadata={"some_data": 10}))
df_new.show()
                
            
            +----------+
|lower_name|
+----------+
|      alex|
|       bob|
|     cathy|
+----------+

The metadata is a dictionary that will be stored in the Column object.

To access the metadata, we can use the PySpark DataFrame's schema property:


        
        
            
                
                
                    df_new.schema["lower_name"].metadata["some_data"]
                
            
            10

Published by Isshin Inada

Edited by 0 others

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Official PySpark Documentation

https://spark.apache.org/docs/3.2.0/api/python/reference/api/pyspark.sql.Column.alias.html

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