ToString

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Transforms every element in an input collection to a string.

Examples

Any non-string element can be converted to a string using standard Python functions and methods. Many I/O transforms, such as textio.WriteToText, expect their input elements to be strings.

Example 1: Key-value pairs to string

The following example converts a (key, value) pair into a string delimited by ','. You can specify a different delimiter using the delimiter argument.

import apache_beam as beam

with beam.Pipeline() as pipeline:
  plants = (
      pipeline
      | 'Garden plants' >> beam.Create([
          ('🍓', 'Strawberry'),
          ('🥕', 'Carrot'),
          ('🍆', 'Eggplant'),
          ('🍅', 'Tomato'),
          ('🥔', 'Potato'),
      ])
      | 'To string' >> beam.ToString.Kvs()
      | beam.Map(print))

Output:

🍓,Strawberry
🥕,Carrot
🍆,Eggplant
🍅,Tomato
🥔,Potato

Example 2: Elements to string

The following example converts a dictionary into a string. The string output will be equivalent to str(element).

import apache_beam as beam

with beam.Pipeline() as pipeline:
  plant_lists = (
      pipeline
      | 'Garden plants' >> beam.Create([
          ['🍓', 'Strawberry', 'perennial'],
          ['🥕', 'Carrot', 'biennial'],
          ['🍆', 'Eggplant', 'perennial'],
          ['🍅', 'Tomato', 'annual'],
          ['🥔', 'Potato', 'perennial'],
      ])
      | 'To string' >> beam.ToString.Element()
      | beam.Map(print))

Output:

['🍓', 'Strawberry', 'perennial']
['🥕', 'Carrot', 'biennial']
['🍆', 'Eggplant', 'perennial']
['🍅', 'Tomato', 'annual']
['🥔', 'Potato', 'perennial']

Example 3: Iterables to string

The following example converts an iterable, in this case a list of strings, into a string delimited by ','. You can specify a different delimiter using the delimiter argument. The string output will be equivalent to iterable.join(delimiter).

import apache_beam as beam

with beam.Pipeline() as pipeline:
  plants_csv = (
      pipeline
      | 'Garden plants' >> beam.Create([
          ['🍓', 'Strawberry', 'perennial'],
          ['🥕', 'Carrot', 'biennial'],
          ['🍆', 'Eggplant', 'perennial'],
          ['🍅', 'Tomato', 'annual'],
          ['🥔', 'Potato', 'perennial'],
      ])
      | 'To string' >> beam.ToString.Iterables()
      | beam.Map(print))

Output:

🍓,Strawberry,perennial
🥕,Carrot,biennial
🍆,Eggplant,perennial
🍅,Tomato,annual
🥔,Potato,perennial
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