topic Nested struct type not supported pyspark error in Data Engineering

Nested struct type not supported pyspark error

kll — Tue, 02 May 2023 03:21:36 GMT

I am attempting to apply a function to a pyspark DataFrame and save the API response to a new column and then parse using `json_normalize`. This works fine in pandas, however, I run into an exception with `pyspark`.

 import pyspark.pandas as ps
 
  import pandas as pd
 
  import requests
 
 
 
 
 
  def get_vals(row):
 
   
 
    # make api call
 
    return row['A'] * row['B']
 
   
 
 
 
  # Create a pandas DataFrame
 
  pdf = pd.DataFrame({'A': [1, 2, 3], 'B': [4, 5, 6]})
 
 
 
 
 
  # apply function - get api responses
 
  pdf['api_response'] = pdf.apply(lambda row: get_vals(row), axis=1)
 
  pdf.sample(5)
 
 
 
  # Unpack JSON API Response
 
  try:
 
    dff = pd.json_normalize(pdf['api_response'].str['location'])
 
  except TypeError as e:
 
    print(f"Error: {e}")
 
    print(f"Problematic data: {data['data']}")
 
 
  # To pySpark DataFrame
 
  psdf = ps.DataFrame(df)
 
  psdf.head(5)

Expected output is a `json` normalized DataFrame. When I attempt to apply the function over a `pyspark` DataFrame, it throws an exception:

psdf['api_response'] = psdf.apply(lambda row: get_vals(row), axis=1)
 
    
 
 ---------------------------------------------------------------------------
 
  TypeError                 Traceback (most recent call last)
 
  File <command-4372401754138893>:2
 
     1 
 
  ----> 2 psdf['api_response'] = psdf.apply(lambda row: get_vals(row), axis=1)
 
   
 
  TypeError: Nested StructType not supported in conversion from Arrow: struct<data: struct<geographies:

Re: Nested struct type not supported pyspark error

Anonymous — Sat, 13 May 2023 15:49:09 GMT

@Keval Shah :

The error message suggests that the issue is with the schema of the psdf DataFrame, specifically with the nested struct type of the api_response column.

Unfortunately, PySpark does not support nested struct types when converting from Arrow format, which is used internally by PySpark DataFrames. As a result, you cannot directly apply a function to a PySpark DataFrame that returns a nested struct type.

One workaround is to use the pandas_udf function in PySpark, which allows you to apply a Pandas UDF (user-defined function) to a PySpark DataFrame. You can define a Pandas UDF that takes a Pandas DataFrame as input, applies the function to the DataFrame, and returns a new Pandas DataFrame with the normalized JSON data. Here's an example of how you can modify your code to use pandas_udf:

import pyspark.sql.functions as F
from pyspark.sql.types import StructType, StructField, DoubleType
 
# Define the schema of the output DataFrame
output_schema = StructType([
    StructField("location.latitude", DoubleType()),
    StructField("location.longitude", DoubleType())
])
 
# Define the function that applies the API call and normalizes the JSON response
def api_call_udf(pdf):
    # Apply the API call to the input Pandas DataFrame
    pdf['api_response'] = pdf.apply(lambda row: get_vals(row), axis=1)
    # Normalize the JSON data using pandas.json_normalize
    normalized_df = pd.json_normalize(pdf['api_response'].str['location'])
    # Return the normalized Pandas DataFrame as an Arrow table
    return normalized_df.to_arrow()
 
# Convert the PySpark DataFrame to a Pandas DataFrame
pdf = psdf.to_pandas()
 
# Apply the function using pandas_udf
normalized_df = psdf.withColumn("output", F.pandas_udf(api_call_udf, output_schema)(F.struct([F.col(x) for x in pdf.columns])))
 
# Convert the output PySpark DataFrame back to a PySpark Pandas DataFrame
psdf_output = ps.DataFrame(normalized_df)

In this code, we define a schema for the output DataFrame and define a function that applies the API call to the input Pandas DataFrame, normalizes the JSON data using pandas.json_normalize, and returns the normalized Pandas DataFrame as an Arrow table. We then convert the PySpark DataFrame to a Pandas DataFrame, apply the function using pandas_udf, and convert the output PySpark DataFrame back to a PySpark Pandas DataFrame.

Re: Nested struct type not supported pyspark error

Anonymous — Fri, 19 May 2023 06:25:47 GMT

Hi @Keval Shah

Thank you for posting your question in our community! We are happy to assist you.

To help us provide you with the most accurate information, could you please take a moment to review the responses and select the one that best answers your question?

This will also help other community members who may have similar questions in the future. Thank you for your participation and let us know if you need any further assistance!