About JSON Data Filtering

Certain pages where JSON data is displayed, such as the state viewer and policy check JSON data viewer, allow you to filter the results. This enables you to see just the data you need, and even create entirely new datasets to see data in the way you want to see it!

Entering a Filter

Filters are entered by putting the filter in the aptly named filter box in the JSON viewer. After entering the filter, pressing Apply or the enter key on your keyboard will apply the filter. The filtered results, if any, are displayed in result box. Clearing the filter will restore the original JSON data.

Filter Language

The JSON filter language is a small subset of the jq JSON filtering language. Selectors, literals, indexes, slices, iterators, and pipes are supported, as are also array and object construction. At this time, parentheses, and more complex operations such as mathematical operators, conditionals, and functions are not supported.

Below is a quick reference of some of the more basic functions to get you started.

Selectors

Selectors allow you to pick an index out of a JSON object, and are written as .KEY.SUBKEY. So, as an example, given an object of {"foo": {"bar": "baz"}}, and the filter .foo.bar, the result would be displayed as "baz".

A single dot (.) without anything else always denotes the current value, unaltered.

Indexes

Indexes can be used to fetch array elements, or select non-alphanumeric object fields. They are written as [0] or ["foo-bar"], depending on the purpose.

Given an object of {"foo-bar": ["baz", "qux"]} and the filter of .["foo-bar"][0], the result would be displayed as "baz".

Slices

Arrays can be sliced to get a subset an array. The syntax is [LOW:HIGH].

Given an array of [0, 1, 2, 3, 4] and the filter of .[1:3], the result would be displayed as [1, 2]. This also illustrates that the result of the slice operation is always of length HIGH-LOW.

Slices can also be applied to strings, in which a substring is returned with the same rules applied, with the first character of the string being index 0.

Iterators

Iterators can iterate over arrays and objects. The syntax is [].

Iterators iterate over the values of an object only. So given a object of {"foo": 1, "bar": 2}, the filter .[] would yield an iteration of 1, 2.

Note that iteration results are not necessarily always arrays. Iterators are handled in a special fashion when dealing with pipes and object creators (see below).

Array Construction

Wrapping an expression in brackets ([ ... ]) creates an array with the sub-expressions inside the array. The results are always concatenated.

For example, for an object of {"foo": [1, 2], "bar": [3, 4]}, the construction expressions [.foo[], .bar[]] and [.[][]], are the same, producing the resulting array [1, 2, 3, 4].

Object Construction

Wrapping an expression in curly braces {KEY: EXPRESSION, ...} creates an object.

Iterators work uniquely with object construction in that an object is constructed for each iteration that the iterator produces.

As a basic example, Consider an array [1, 2, 3]. While the expression {foo: .} will produce {"foo": [1, 2, 3]}, adding an iterator to the expression so that it reads {foo: .[]} will produce 3 individual objects: {"foo": 1}, {"foo": 2}, and {"foo": 3}.

Pipes

Pipes allow the results of one expression to be fed into another. This can be used to re-write expressions to help reduce complexity.

Iterators work with pipes in a fashion similar to object construction, where the expression on the right-hand side of the pipe is evaluated once for every iteration.

As an example, for the object {"foo": {"a": 1}, "bar": {"a": 2}}, both the expression {z: .[].a} and .[] | {z: .a} produce the same result: {"z": 1} and {"z": 2}.