YAML Multi-Line Arrays

181
votes

In YAML, you can easily create multi-line strings. However, I would like the ability to create a multi-line array (mainly for readibility within config files) using the | character.

A YAML array can be represented as: ['key1', 'key2', 'key3'].

A YAML sequence uses a dash followed by a space and then a string:

- String1
- String2
- String3

This would evaluate to: ['string1', 'string2', 'string3'].

A YAML mapping is an array of key and value pairs that we see all the time in YAML:

Key1: string1
Key2: string2
Key3: string3

This is all well and good, but I can't for the life of me see how to do a multi-line array. Something like this:

|
['string1', 'string2', 'string3']
['string4', 'string5', 'string6']

Short of creating multiple array mappings in YAML and merging them in my programming language of choice, is there any way to achieve multi-line arrays, maybe with { } like Python has but in YAML?

5
yaml
honestly, whats a multi-line array & when should it be meaningful at all? Rather than just the looks of your code – OK999
Having to scroll across the screen horizontally to see all the options rather than see them all one one screen at once. – Jimbo
Multi-line may make diffs much more readable, since every item added or removed corresponds to 1 line added or removed. – XedinUnknown
@XedinUnknown Good technical argument and reasoning - version control usage is impacted less with future changes. Thanks for sharing. – Jimbo

5 Answers

320
votes

A YAML sequence is an array. So this is the right way to express it:

key:
  - string1
  - string2      
  - string3
  - string4
  - string5
  - string6

That's identical in meaning to:

key: ['string1', 'string2', 'string3', 'string4', 'string5', 'string6']

It's also legal to split a single-line array over several lines:

key: ['string1', 'string2', 'string3', 
  'string4', 'string5', 
  'string6']

and even have multi-line strings in single-line arrays:

key: ['string1', 'long
  string', 'string3', 'string4', 'string5', 'string6']
62
votes

have you tried this?

-
  name: Jack
  age: 32
-
  name: Claudia
  age: 25

I get this: [{"name"=>"Jack", "age"=>32}, {"name"=>"Claudia", "age"=>25}] (I use the YAML Ruby class).

8
votes

The following would work:

myarray: [
  String1, String2, String3,
  String4, String5, String5, String7
]

I tested it using the snakeyaml implementation, I am not sure about other implementations though.

6
votes

If what you are needing is an array of arrays, you can do this way:

key:
  - [ 'value11', 'value12', 'value13' ]
  - [ 'value21', 'value22', 'value23' ]
4
votes

The following works for me and its good from readability point of view when the number of array element values is small:

key: [string1, string2, string3, string4, string5, string6]

This has been tested to work with snakeyaml and ruamel.yaml.