Databricks Updated Databricks-Machine-Learning-Associate Exam Questions and Answers by syeda

To filter rows in a Spark DataFrame based on a condition, thefiltermethod is used. In this case, the condition is that the value in the "discount" column should be less than or equal to 0. The correct syntax uses thefiltermethod along with thecolfunction frompyspark.sql.functions.

Correct code:

frompyspark.sql.functionsimportcol filtered_df = spark_df.filter(col("discount") <=0)

Option A and D use Pandas syntax, which is not applicable in PySpark. Option B is closer but misses the use of thecolfunction.

References:

• PySpark SQL Documentation

The Root Mean Squared Error (RMSE) is a standard and widely used metric for evaluating the accuracy of regression models. The statement that it is invalid is incorrect. Here’s a breakdown of why the other statements are or are not valid:

• Transformations and RMSE Calculation:If the model predictions were transformed (e.g., using log), they should be converted back to their original scale before calculating RMSE to ensure accuracy in the evaluation. Missteps in this conversion process can lead to misleading RMSE values.
• Accuracy of Models:Without additional information, we can't definitively say which model is more accurate without considering their RMSE values properly scaled back to the original price scale.
• Appropriateness of RMSE:RMSE is entirely valid for regression problems as it provides a measure of how accurately a model predicts the outcome, expressed in the same units as the dependent variable.

References

• "Applied Predictive Modeling" by Max Kuhn and Kjell Johnson (Springer, 2013), particularly the chapters discussing model evaluation metrics.

In the provided code block, theImputerobject is created but not fitted on the data to generate anImputerModel. Thetransformmethod is being called directly on theImputerobject, which does not yet contain the fitted median values needed for imputation. The correct approach is to fit the imputer on the dataset first.

Corrected code:

imputer = Imputer( strategy="median", inputCols=input_columns, outputCols=output_columns ) imputer_model = imputer.fit(features_df)# Fit the imputer to the dataimputed_features_df = imputer_model.transform(features_df)# Transform the data using the fitted imputer

References:

• PySpark ML Documentation

Among the options listed, calculating the true median for imputing missing feature values is the least efficient to distribute. This is because the true median requires knowledge of the entire data distribution, which can be computationally expensive in a distributed environment. Unlike mean or mode, finding the median requires sorting the data or maintaining a full distribution, which is more intensive and often requires shuffling the data across partitions.

References

• Challenges in parallel processing and distributed computing for data aggregation like median calculation:https://www.apache.org