YAML collections: Sequences and mappings

By Syed Wahaj

Introduction

YAML (YAML Ain’t Markup Language) is a human-readable data serialization format. It provides support for various data structures, including collections like sequences and mappings. In this article, we will explore YAML collections in detail, covering sequences, mappings, and other types.

1. Understanding YAML Collections

YAML collections allow you to represent groups of related data. They provide a structured way to organize and store multiple values. YAML supports two primary collection types: sequences and mappings.

2. Sequences

Sequences in YAML represent ordered lists of items. Each item in a sequence is preceded by a hyphen (-) and can be of any data type. Sequences allow for the representation of lists, arrays, or sets of values.

fruits:
  - apple
  - banana
  - mango

In the above example, the “fruits” sequence contains three items: “apple,” “banana,” and “mango.”

3. Mappings

Mappings in YAML represent key-value pairs, similar to dictionaries or hash tables. Mappings use a colon (:) to separate keys and values. The key-value pairs can be of any data type.

person:
  name: John Doe
  age: 30
  city: New York

In the above example, the “person” mapping contains three key-value pairs: “name” with the value “John Doe,” “age” with the value 30, and “city” with the value “New York.”

4. Nested Collections

YAML allows nesting of collections within other collections. This enables the representation of complex data structures. Sequences can contain mappings, and mappings can contain sequences or other mappings.

users:
  - name: John Doe
    age: 30
  - name: Jane Smith
    age: 25

In the above example, the “users” sequence contains two mappings, each representing a user with “name” and “age” keys.

5. Scalars Scalars are atomic values in YAML, representing single values of various types such as strings, numbers, booleans, and null.

name: John Doe
age: 30
isStudent: true

In the above example, “name” is a string scalar, “age” is a numeric scalar, and “isStudent” is a boolean scalar.

6. Anchors and Aliases

YAML allows the use of anchors and aliases to reference values within the same YAML document. Anchors use an ampersand (&), and aliases use an asterisk (*) followed by the anchor name.

fruits:
  - &apple apple
  - banana
  - *apple

In the above example, the first item in the “fruits” sequence is anchored as “apple.” The third item is then aliased to the anchored value, creating a reference to “apple.”

7. Flow Collections

YAML also provides flow collections, which are compact representations of sequences and mappings. Flow sequences use brackets ([ and ]), while flow mappings use curly braces ({ and }). Flow collections are useful for representing data in a more concise manner.

fruits: [apple, banana, mango]

person: { name: John Doe, age: 30, city: New York }

In the above example, the flow sequence represents the “fruits” sequence, and the flow mapping represents the “person” mapping.

8. Collections as Values

Collections can be used as values within mappings, allowing for more complex data structures.

users:
  - name: John Doe
    fruits: [apple, banana, mango]
  - name: Jane Smith
    fruits: [orange, strawberry]

In the above example, each user in the “users” sequence has a name and a fruits sequence as a value.

Conclusion

In this comprehensive guide, we explored YAML collections, including sequences, mappings, and other types. We learned that sequences represent ordered lists of items, while mappings represent key-value pairs. Sequences are denoted by a hyphen (-) preceding each item, while mappings use a colon (:) to separate keys and values.

Nested collections allow for the representation of complex data structures, where sequences can contain mappings and mappings can contain sequences or other mappings. Scalars represent atomic values such as strings, numbers, booleans, and null.

Anchors and aliases provide a way to reference values within the same YAML document, allowing for reusability and avoiding repetition. Flow collections, represented by brackets ([ and ]) for sequences and curly braces ({ and }) for mappings, offer a more compact representation of data.

Finally, we explored how collections can be used as values within mappings, allowing for the creation of more complex and structured data structures.

By mastering YAML collections and their various features, you can effectively represent and organize data in YAML documents, making them more readable, maintainable, and flexible. YAML’s simplicity and human-readable syntax make it a popular choice for configuration files, data serialization, and interchanging data between different systems.

Remember to follow the YAML specifications and best practices when working with collections to ensure proper formatting, readability, and compatibility with YAML parsers and processors.

In conclusion, YAML collections provide a powerful and flexible way to structure and organize data. Whether you are working with simple lists or complex nested structures, understanding and utilizing YAML collections will enable you to effectively represent data in YAML format and make the most out of this popular serialization language.