Deploying a Dataflow Pipeline using Python and Apache Beam

Question

I am new to using Apache Beam and Dataflow. I would like to use a data-set as an input for a function that will be deployed in parallel using Dataflow. Here is what I have so far:

import os
import apache_beam as beam
from apache_beam.options.pipeline_options import SetupOptions
from apache_beam.options.pipeline_options import PipelineOptions
from apache_beam.options.pipeline_options import StandardOptions
from apache_beam.options.pipeline_options import GoogleCloudOptions

os.environ['GOOGLE_APPLICATION_CREDENTIALS'] = '[location of json service credentails]'

dataflow_options = ['--project=[PROJECT NAME]',
                    '--job_name=[JOB NAME]',
                    '--temp_location=gs://[BUCKET NAME]/temp',
                    '--staging_location=gs://[BUCKET NAME]/stage']
options = PipelineOptions(dataflow_options)
gcloud_options = options.view_as(GoogleCloudOptions)
options.view_as(StandardOptions).runner = 'dataflow'

with beam.Pipeline(options=options) as p:
     new_p = p | beam.io.ReadFromText(file_pattern='[file location].csv',
                                      skip_header_lines=1)
               | beam.ParDo([Function Name]())

The CSV file will have 4 columns with n rows. Each row represents an instance and each column represents a parameter of that instance. I would like to slip all of the parameters of an instance into a beam.DoFn so I can run it on multiple machines with the help of dataflow.

How do I get a write the function to take multiple arguments from a PCollection? The function below is how I imagine it would go.

class function_name(beam.DoFn):
    def process(self, col_1, col_2, col_3, col_4):
    function = function(col_1) + function(col_2) + function(col_3) + function(col_4)
    return [function]

Beam has the concept of PCollection consisting of element, in your example the csv file is read line-by-line and each line will be an element that will be mapped implicitly to your callable inside the ParDo step. You don't need multiple arguments in your process method, you just need a single argument, which in this case will be a string e.g. "col1_value, col2_value, col3_value, col4_value" which you will need to split and process and return as a new single element. If you want to return multiple values, use a tuple, dict or some other collection as your return element. — Davos
– Davos, Commented Jan 7, 2019 at 10:59

Eric Schmidt · Accepted Answer · 2018-11-21 18:35:08Z

2

The materialized return from ReadFromText will be a PCollection where the string is still delimited.

Your ParDo should take an element of String and then do a split which you could yield as Dict of col name and value.

answered Nov 21, 2018 at 18:35

Eric Schmidt

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