Code example: Data preparation using ResolveChoice, Lambda, and ApplyMapping - Amazon Glue
Step 1: Crawl the dataStep 2: Add boilerplate scriptStep 3: Compare schemas4. apply mappingStep 5: Write to Parquet
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Code example: Data preparation using ResolveChoice, Lambda, and ApplyMapping

The dataset that is used in this example consists of Medicare Provider payment data that was downloaded from two Data.CMS.gov data sets: "Inpatient Prospective Payment System Provider Summary for the Top 100 Diagnosis-Related Groups - FY2011" and "Inpatient Charge Data FY 2011". After downloading the data, we modified the dataset to introduce a couple of erroneous records at the end of the file. This modified file is located in a public Amazon S3 bucket at s3://awsglue-datasets/examples/medicare/Medicare_Hospital_Provider.csv.

You can find the source code for this example in the data_cleaning_and_lambda.py file in the Amazon Glue examples GitHub repository.

The preferred way to debug Python or PySpark scripts while running on Amazon is to use Notebooks on Amazon Glue Studio.

Step 1: Crawl the data in the Amazon S3 bucket

  1. Sign in to the Amazon Web Services Management Console and open the Amazon Glue console at https://console.amazonaws.cn/glue/.

  2. Following the process described in Configuring a crawler, create a new crawler that can crawl the s3://awsglue-datasets/examples/medicare/Medicare_Hospital_Provider.csv file, and can place the resulting metadata into a database named payments in the Amazon Glue Data Catalog.

  3. Run the new crawler, and then check the payments database. You should find that the crawler has created a metadata table named medicare in the database after reading the beginning of the file to determine its format and delimiter.

    The schema of the new medicare table is as follows:

    Column  name                            Data type
==================================================
drg definition                             string
provider id                                bigint
provider name                              string
provider street address                    string
provider city                              string
provider state                             string
provider zip code                          bigint
hospital referral region description       string
total discharges                           bigint
average covered charges                    string
average total payments                     string
average medicare payments                  string

Step 2: Add boilerplate script to the development endpoint notebook

Paste the following boilerplate script into the development endpoint notebook to import the Amazon Glue libraries that you need, and set up a single GlueContext:

import sys
from awsglue.transforms import *
from awsglue.utils import getResolvedOptions
from pyspark.context import SparkContext
from awsglue.context import GlueContext
from awsglue.job import Job

glueContext = GlueContext(SparkContext.getOrCreate())

Step 3: Compare different schema parsings

Next, you can see if the schema that was recognized by an Apache Spark DataFrame is the same as the one that your Amazon Glue crawler recorded. Run this code:


medicare = spark.read.format(
   "com.databricks.spark.csv").option(
   "header", "true").option(
   "inferSchema", "true").load(
   's3://awsglue-datasets/examples/medicare/Medicare_Hospital_Provider.csv')
medicare.printSchema()

Here's the output from the printSchema call:


root
 |-- DRG Definition: string (nullable = true)
 |-- Provider Id: string (nullable = true)
 |-- Provider Name: string (nullable = true)
 |-- Provider Street Address: string (nullable = true)
 |-- Provider City: string (nullable = true)
 |-- Provider State: string (nullable = true)
 |-- Provider Zip Code: integer (nullable = true)
 |-- Hospital Referral Region Description: string (nullable = true)
 |--  Total Discharges : integer (nullable = true)
 |--  Average Covered Charges : string (nullable = true)
 |--  Average Total Payments : string (nullable = true)
 |-- Average Medicare Payments: string (nullable = true)

Next, look at the schema that an Amazon Glue DynamicFrame generates:


medicare_dynamicframe = glueContext.create_dynamic_frame.from_catalog(
       database = "payments",
       table_name = "medicare")
medicare_dynamicframe.printSchema()

The output from printSchema is as follows:


root
 |-- drg definition: string
 |-- provider id: choice
 |    |-- long
 |    |-- string
 |-- provider name: string
 |-- provider street address: string
 |-- provider city: string
 |-- provider state: string
 |-- provider zip code: long
 |-- hospital referral region description: string
 |-- total discharges: long
 |-- average covered charges: string
 |-- average total payments: string
 |-- average medicare payments: string

The DynamicFrame generates a schema in which provider id could be either a long or a string type. The DataFrame schema lists Provider Id as being a string type, and the Data Catalog lists provider id as being a bigint type.

Which one is correct? There are two records at the end of the file (out of 160,000 records) with string values in that column. These are the erroneous records that were introduced to illustrate a problem.

To address this kind of problem, the Amazon Glue DynamicFrame introduces the concept of a choice type. In this case, the DynamicFrame shows that both long and string values can appear in that column. The Amazon Glue crawler missed the string values because it considered only a 2 MB prefix of the data. The Apache Spark DataFrame considered the whole dataset, but it was forced to assign the most general type to the column, namely string. In fact, Spark often resorts to the most general case when there are complex types or variations with which it is unfamiliar.

To query the provider id column, resolve the choice type first. You can use the resolveChoice transform method in your DynamicFrame to convert those string values to long values with a cast:long option:


medicare_res = medicare_dynamicframe.resolveChoice(specs = [('provider id','cast:long')])
medicare_res.printSchema()

The printSchema output is now:

root
 |-- drg definition: string
 |-- provider id: long
 |-- provider name: string
 |-- provider street address: string
 |-- provider city: string
 |-- provider state: string
 |-- provider zip code: long
 |-- hospital referral region description: string
 |-- total discharges: long
 |-- average covered charges: string
 |-- average total payments: string
 |-- average medicare payments: string

Where the value was a string that could not be cast, Amazon Glue inserted a null.

Another option is to convert the choice type to a struct, which keeps values of both types.

Next, look at the rows that were anomalous:


medicare_res.toDF().where("'provider id' is NULL").show()

You see the following:


+--------------------+-----------+---------------+-----------------------+-------------+--------------+-----------------+------------------------------------+----------------+-----------------------+----------------------+-------------------------+
|      drg definition|provider id|  provider name|provider street address|provider city|provider state|provider zip code|hospital referral region description|total discharges|average covered charges|average total payments|average medicare payments|
+--------------------+-----------+---------------+-----------------------+-------------+--------------+-----------------+------------------------------------+----------------+-----------------------+----------------------+-------------------------+
|948 - SIGNS & SYM...|       null|            INC|       1050 DIVISION ST|      MAUSTON|            WI|            53948|                        WI - Madison|              12|              $11961.41|              $4619.00|                 $3775.33|
|948 - SIGNS & SYM...|       null| INC- ST JOSEPH|     5000 W CHAMBERS ST|    MILWAUKEE|            WI|            53210|                      WI - Milwaukee|              14|              $10514.28|              $5562.50|                 $4522.78|
+--------------------+-----------+---------------+-----------------------+-------------+--------------+-----------------+------------------------------------+----------------+-----------------------+----------------------+-------------------------+

Now remove the two malformed records, as follows:

medicare_dataframe = medicare_res.toDF()
medicare_dataframe = medicare_dataframe.where("'provider id' is NOT NULL")

Step 4: Map the data and use Apache Spark Lambda functions

Amazon Glue does not yet directly support Lambda functions, also known as user-defined functions. But you can always convert a DynamicFrame to and from an Apache Spark DataFrame to take advantage of Spark functionality in addition to the special features of DynamicFrames.

Next, turn the payment information into numbers, so analytic engines like Amazon Redshift or Amazon Athena can do their number crunching faster:

from pyspark.sql.functions import udf
from pyspark.sql.types import StringType

chop_f = udf(lambda x: x[1:], StringType())
medicare_dataframe = medicare_dataframe.withColumn(
        "ACC", chop_f(
            medicare_dataframe["average covered charges"])).withColumn(
                "ATP", chop_f(
                    medicare_dataframe["average total payments"])).withColumn(
                        "AMP", chop_f(
                            medicare_dataframe["average medicare payments"]))
medicare_dataframe.select(['ACC', 'ATP', 'AMP']).show()

The output from the show call is as follows:

+--------+-------+-------+
|     ACC|    ATP|    AMP|
+--------+-------+-------+
|32963.07|5777.24|4763.73|
|15131.85|5787.57|4976.71|
|37560.37|5434.95|4453.79|
|13998.28|5417.56|4129.16|
|31633.27|5658.33|4851.44|
|16920.79|6653.80|5374.14|
|11977.13|5834.74|4761.41|
|35841.09|8031.12|5858.50|
|28523.39|6113.38|5228.40|
|75233.38|5541.05|4386.94|
|67327.92|5461.57|4493.57|
|39607.28|5356.28|4408.20|
|22862.23|5374.65|4186.02|
|31110.85|5366.23|4376.23|
|25411.33|5282.93|4383.73|
| 9234.51|5676.55|4509.11|
|15895.85|5930.11|3972.85|
|19721.16|6192.54|5179.38|
|10710.88|4968.00|3898.88|
|51343.75|5996.00|4962.45|
+--------+-------+-------+
only showing top 20 rows

These are all still strings in the data. We can use the powerful apply_mapping transform method to drop, rename, cast, and nest the data so that other data programming languages and systems can easily access it:

from awsglue.dynamicframe import DynamicFrame
medicare_tmp_dyf = DynamicFrame.fromDF(medicare_dataframe, glueContext, "nested")
medicare_nest_dyf = medicare_tmp_dyf.apply_mapping([('drg definition', 'string', 'drg', 'string'),
                 ('provider id', 'long', 'provider.id', 'long'),
                 ('provider name', 'string', 'provider.name', 'string'),
                 ('provider city', 'string', 'provider.city', 'string'),
                 ('provider state', 'string', 'provider.state', 'string'),
                 ('provider zip code', 'long', 'provider.zip', 'long'),
                 ('hospital referral region description', 'string','rr', 'string'),
                 ('ACC', 'string', 'charges.covered', 'double'),
                 ('ATP', 'string', 'charges.total_pay', 'double'),
                 ('AMP', 'string', 'charges.medicare_pay', 'double')])
medicare_nest_dyf.printSchema()

The printSchema output is as follows:

root
 |-- drg: string
 |-- provider: struct
 |    |-- id: long
 |    |-- name: string
 |    |-- city: string
 |    |-- state: string
 |    |-- zip: long
 |-- rr: string
 |-- charges: struct
 |    |-- covered: double
 |    |-- total_pay: double
 |    |-- medicare_pay: double

Turning the data back into a Spark DataFrame, you can show what it looks like now:

medicare_nest_dyf.toDF().show()

The output is as follows:

+--------------------+--------------------+---------------+--------------------+
|                 drg|            provider|             rr|             charges|
+--------------------+--------------------+---------------+--------------------+
|039 - EXTRACRANIA...|[10001,SOUTHEAST ...|    AL - Dothan|[32963.07,5777.24...|
|039 - EXTRACRANIA...|[10005,MARSHALL M...|AL - Birmingham|[15131.85,5787.57...|
|039 - EXTRACRANIA...|[10006,ELIZA COFF...|AL - Birmingham|[37560.37,5434.95...|
|039 - EXTRACRANIA...|[10011,ST VINCENT...|AL - Birmingham|[13998.28,5417.56...|
|039 - EXTRACRANIA...|[10016,SHELBY BAP...|AL - Birmingham|[31633.27,5658.33...|
|039 - EXTRACRANIA...|[10023,BAPTIST ME...|AL - Montgomery|[16920.79,6653.8,...|
|039 - EXTRACRANIA...|[10029,EAST ALABA...|AL - Birmingham|[11977.13,5834.74...|
|039 - EXTRACRANIA...|[10033,UNIVERSITY...|AL - Birmingham|[35841.09,8031.12...|
|039 - EXTRACRANIA...|[10039,HUNTSVILLE...|AL - Huntsville|[28523.39,6113.38...|
|039 - EXTRACRANIA...|[10040,GADSDEN RE...|AL - Birmingham|[75233.38,5541.05...|
|039 - EXTRACRANIA...|[10046,RIVERVIEW ...|AL - Birmingham|[67327.92,5461.57...|
|039 - EXTRACRANIA...|[10055,FLOWERS HO...|    AL - Dothan|[39607.28,5356.28...|
|039 - EXTRACRANIA...|[10056,ST VINCENT...|AL - Birmingham|[22862.23,5374.65...|
|039 - EXTRACRANIA...|[10078,NORTHEAST ...|AL - Birmingham|[31110.85,5366.23...|
|039 - EXTRACRANIA...|[10083,SOUTH BALD...|    AL - Mobile|[25411.33,5282.93...|
|039 - EXTRACRANIA...|[10085,DECATUR GE...|AL - Huntsville|[9234.51,5676.55,...|
|039 - EXTRACRANIA...|[10090,PROVIDENCE...|    AL - Mobile|[15895.85,5930.11...|
|039 - EXTRACRANIA...|[10092,D C H REGI...|AL - Tuscaloosa|[19721.16,6192.54...|
|039 - EXTRACRANIA...|[10100,THOMAS HOS...|    AL - Mobile|[10710.88,4968.0,...|
|039 - EXTRACRANIA...|[10103,BAPTIST ME...|AL - Birmingham|[51343.75,5996.0,...|
+--------------------+--------------------+---------------+--------------------+
only showing top 20 rows

Step 5: Write the data to Apache Parquet

Amazon Glue makes it easy to write the data in a format such as Apache Parquet that relational databases can effectively consume:

glueContext.write_dynamic_frame.from_options(
       frame = medicare_nest_dyf,
       connection_type = "s3",
       connection_options = {"path": "s3://glue-sample-target/output-dir/medicare_parquet"},
       format = "parquet")