Ndtyjky

The Spark Pipeline framework allows for creation of pipelines of transforms for machine learning or other applications in a reproducible way. However, when creating the dataframes, I want to be able to perform exploratory analysis.

In my case, I have ~100 columns, of which 80 are strings and need to be one hot encoded:

from pyspark.ml.feature import OneHotEncoderEstimator, StringIndexer,VectorAssembler

from pyspark.ml import Pipeline

from pyspark.ml.classification import LogisticRegression

from pyspark.ml.classification import LogisticRegressionModel



#cols_to_one_hot_encode_2 is a list of columns that need to be one hot encoded

#cols_to_keep_as_is are columns that are **note** one hot encoded



cols_to_one_hot_encode_3=[i+"_hot" for i in cols_to_one_hot_encode_2]

encoder= OneHotEncoderEstimator(inputCols=cols_to_one_hot_encode_2,

                                 outputCols=cols_to_one_hot_encode_3,dropLast=False)



#assemble pipeline

vectorAssembler = VectorAssembler().setInputCols(cols_to_keep_as_is+cols_to_one_hot_encode_3).setOutputCol("features")

all_stages=indexers

all_stages.append(encoder)

all_stages.append(vectorAssembler)

transformationPipeline=Pipeline(stages=all_stages)

fittedPipeline=transformationPipeline.fit(df_3)

dataset = fittedPipeline.transform(df_3)



#now pass to logistic regression

selectedcols = ["response_variable","features"] #+df_3.columns

dataset_2= dataset.select(selectedcols)



# Create initial LogisticRegression model

lr = LogisticRegression(labelCol="response_variable", featuresCol="features", maxIter=10,elasticNetParam=1)



# Train model with Training Data

lrModel = lr.fit(dataset_2)

When I look at dataset_2 display(dataset_2), it prints:

response_variable       features

0   [0,6508,[1,4,53,155,166,186,205,242,2104,6225,6498],[8220,1,1,1,1,1,1,1,1,1,1]]

0   [0,6508,[1,3,53,155,165,185,207,243,2104,6225,6498],[8220,1,1,1,1,1,1,1,1,1,1]]

0   [0,6508,[1,2,53,158,170,185,206,241,2104,6225,6498],[8222,1,1,1,1,1,1,1,1,1,1]]

0   [0,6508,[1,3,53,156,168,185,205,240,2104,6225,6498],[8222,1,1,1,1,1,1,1,1,1,1]]

0   [0,6508,[1,2,53,155,166,185,205,240,2104,6225,6498],[8223,1,1,1,1,1,1,1,1,1,1]]

Which is totally useless for doing feature exploration.Notice that the one-hot encoder has exploded my features from ~100 columns to 6508.

My question

How do I look at the dataframe that iscreated under the hood by the pipeline?
This should be a dataframe that has 6058 features and the corresponding number of rows, such as:
For example, I want something like:

response_variable    feature_1_hot_1 feature_1_hot_2  feature_1_hot_3 ... (6505 more columns)

0                    1               1                0



etc.

Not a duplicate

Not a duplicate of How to split Vector into columns - using PySpark
That is asking how to do literal string splitting based on a delimiter. The transform done by the pipeline is not a simple string splitting. See Using Spark ML Pipelines just for Transformations

How do I look at the dataframe that iscreated under the hood by the pipeline?

There is no such hidden structure. Spark ML Pipelines are build around VectorUDT columns and metadata to enrich the structure. There is no intermediate structure that holds expanded columns, and if there where, it wouldn't scale (Spark doesn't handle wide and dense data that would be generated here, and query planner chokes when number of columns gets into tens of thousands) given the current implementation.

Splitting the columns and analyzing the metadata is your best and only option.