Skip to content
6.3.6. Ellipse Path

6.3.6. Ellipse Path

Path queries over ellipse objects.

Inspired by jq simple selectors, but over elps objects! This library allows concise and easy manipulation of elps data. parse_tests.go has a comprehensive set of tests to demonstrate typical queries. You can readily compare these results against jq using the jq playground:

We only support simple selectors that output a single value. All paths are strings that must begin with . A path consists of a series of selectors, and performs operations (both mutating and non-mutating versions): 1) Get, 2) Set, 3) Delete, 4) Nil. These operations take ELPS LVals as input, and return an elps LVal.

In the below examples we use JSON to represent elps data structures.

Index & Dot Selectors

Index and dot examples: .regularKey, ["$special key"], [0]

Object: {"hello":"world"}

Path: .hello

Output: "world"

Range Selectors

Range examples: [1:2], [:2], [1:], [:]

Object: ["a","b","c"]

Get Path: .[1:]

Output: ["b","c"]

Iterator Selectors

Iterator selectors execute a path selector on each element of an array.

Object: {"a":[ { "b": 2 }, 0, {"b": 3 } ] }

Get Path: .a[].b

Output: [2,null,3]

Note: jq would throw an error since .b on 0 is an error, however elpspath iterators returns null when the selector throws an error.

Like in jq, nested iterators are collapsed in the return results:

Object: [ {"a":[ { "b": 2 }, {"b": 3 } ] }, {"a":[ { "b": 4 } ]} ]

Get Path: .[].a[].b Output: [2,3,4]

Differences from jq

  • Range selectors such as [:2] is treated as a query of two paths: [0], [1], where the query results are wrapped in array [...]
  • elpspath supports [:] notation which is equivalent to [0:].
  • Iterator notation [] will skip over some errors that jq will throw an error.
  • jq iterators have a notation of "multiple outputs" where each output of an iterator is printed on a new line. elpspath iterators return multiple outputs wrapped in an array, as jq would if there was an outer braces [a[].b] array constructor surrounding the iterator query.

We use cookies to give you the best experience of using this website. By continuing to use this site, you accept our use of cookies. Please read our Cookie Policy for more information.