在 Dataflow 作业中查找重复项 - Python

Question

我想用这个例子创建一个工作流：

https://github.com/GoogleCloudPlatform/professional-services/tree/master/examples/cloud-composer-examples/composer_dataflow_examples

我想做完全相同的事情，并且我已经创建了所有脚本，但我需要对 Dataflow 作业进行一些修改，以检查 CSV 中是否有任何我想要提取到 Bigquery 中的重复值。

这是数据流代码：

    """dataflow_job.py is a Dataflow pipeline which reads a delimited file,
    adds some additional metadata fields and loads the contents to a BigQuery table."""


    import argparse
    import logging
    import ntpath
    import re

    import apache_beam as beam
    from apache_beam.options import pipeline_options


    class RowTransformer(object):
        """A helper class that contains utility methods to parse the delimited file
        and convert every record into a format acceptable to BigQuery. It also contains
        utility methods to add a load_dt and a filename fields as demonstration of
        how records can be enriched as part of the load process."""

        def __init__(self, delimiter, header, filename, load_dt):
            self.delimiter = delimiter

            # Extract the field name keys from the comma separated input.
            self.keys = re.split(',', header)

            self.filename = filename
            self.load_dt = load_dt

        def parse(self, row):
            """This method translates a single delimited record into a dictionary
            which can be loaded into BigQuery. It also adds filename and load_dt
            fields to the dictionary."""

            # Strip out the return characters and quote characters.
            values = re.split(self.delimiter, re.sub(r'[\r\n"]', '', row))

            row = dict(list(zip(self.keys, values)))

            # Add an additional filename field.
            row['filename'] = self.filename

            # Add an additional load_dt field.
            row['load_dt'] = self.load_dt

            return row


    def run(argv=None):
        """The main function which creates the pipeline and runs it."""
        parser = argparse.ArgumentParser()

        # Add the arguments needed for this specific Dataflow job.
        parser.add_argument(
            '--input', dest='input', required=True,
            help='Input file to read.  This can be a local file or '
                'a file in a Google Storage Bucket.')

        parser.add_argument('--output', dest='output', required=True,
                            help='Output BQ table to write results to.')

        parser.add_argument('--delimiter', dest='delimiter', required=False,
                            help='Delimiter to split input records.',
                            default=',')

        parser.add_argument('--fields', dest='fields', required=True,
                            help='Comma separated list of field names.')

        parser.add_argument('--load_dt', dest='load_dt', required=True,
                            help='Load date in YYYY-MM-DD format.')

        known_args, pipeline_args = parser.parse_known_args(argv)
        row_transformer = RowTransformer(delimiter=known_args.delimiter,
                                        header=known_args.fields,
                                        filename=ntpath.basename(known_args.input),
                                        load_dt=known_args.load_dt)

        p_opts = pipeline_options.PipelineOptions(pipeline_args)

        # Initiate the pipeline using the pipeline arguments passed in from the
        # command line.  This includes information including where Dataflow should
        # store temp files, and what the project id is.
        with beam.Pipeline(options=p_opts) as pipeline:
            # Read the file.  This is the source of the pipeline.  All further
            # processing starts with lines read from the file.  We use the input
            # argument from the command line.
            rows = pipeline | "Read from text file" >> beam.io.ReadFromText(known_args.input)

            # This stage of the pipeline translates from a delimited single row
            # input to a dictionary object consumable by BigQuery.
            # It refers to a function we have written.  This function will
            # be run in parallel on different workers using input from the
            # previous stage of the pipeline.
            dict_records = rows | "Convert to BigQuery row" >> beam.Map(
                lambda r: row_transformer.parse(r))

            # This stage of the pipeline writes the dictionary records into
            # an existing BigQuery table. The sink is also configured to truncate
            # the table if it contains any existing records.
            dict_records | "Write to BigQuery" >> beam.io.Write(
                beam.io.BigQuerySink(known_args.output,
                                    create_disposition=beam.io.BigQueryDisposition.CREATE_NEVER,
                                    write_disposition=beam.io.BigQueryDisposition.WRITE_APPEND))


    if __name__ == '__main__':
        logging.getLogger().setLevel(logging.INFO)
        run()

我使用 Apache Beam 的经验非常有限，我如何添加另一个函数来检查我的 Rowtransformer 创建的字典的值是否有任何重复项？

Answer 1

您可以使用Distinct 函数删除重复项。详情可见here

rows = pipeline | "Read from text file" >> beam.io.ReadFromText(known_args.input)
                | "Remove Duplicates"   >> beam.Distinct()

dict_records = rows | "Convert to BigQuery row" >> beam.Map(
                lambda r: row_transformer.parse(r))

...

Answer 2

Beam 提供了一种与其他方法（Spark/pandas..）一样工作的 drop duplicates 方法 Method link

所以你可以这样做：

rows = pipeline | "Read from text file" >> beam.io.ReadFromText(known_args.input)
                | "Remove Duplicates"   >> beam.RemoveDuplicates()