JMESPath · lesson 14 of 15 · Functions

Strings, join & map

join(glue, list) builds a string, and map(&expr, list) applies an expression to every element.

Example 1Join names into one string

Document

{
  "team": "Platform",
  "office": { "city": "Berlin", "floor": 3 },
  "members": [
    { "name": "Ada", "age": 36, "role": "lead", "active": true,
      "email": "[email protected]", "skills": ["rust", "sql"] },
    { "name": "Linus", "age": 28, "role": "dev", "active": true,
      "email": null, "skills": ["c", "shell"] },
    { "name": "Grace", "age": 45, "role": "dev", "active": false,
      "skills": ["cobol"] },
    { "name": "Alan", "age": 41, "role": "qa", "active": true,
      "email": "[email protected]", "skills": [] }
  ]
}

Query

join(', ', members[*].name)

join( Glue a list of strings into one string.
', ' The separator (a raw string).
members[*].name The list to join.

Result

"Ada, Linus, Grace, Alan"

Try it in the playground

Example 2Apply an expression to each element

Document

{
  "team": "Platform",
  "office": { "city": "Berlin", "floor": 3 },
  "members": [
    { "name": "Ada", "age": 36, "role": "lead", "active": true,
      "email": "[email protected]", "skills": ["rust", "sql"] },
    { "name": "Linus", "age": 28, "role": "dev", "active": true,
      "email": null, "skills": ["c", "shell"] },
    { "name": "Grace", "age": 45, "role": "dev", "active": false,
      "skills": ["cobol"] },
    { "name": "Alan", "age": 41, "role": "qa", "active": true,
      "email": "[email protected]", "skills": [] }
  ]
}

Query

map(&length(skills), members)

map( Run an expression on every element of a list and collect the results.
&length(skills) The expression, as a reference: how many skills each one has.
members The list to map over → [2,2,1,0].

Result

[2,2,1,0]

Try it in the playground

Good to know

contains, starts_with, ends_with, length and reverse work on strings too: reverse('abc') is "cba".