> ## Documentation Index > Fetch the complete documentation index at: https://docs.pixeltable.com/llms.txt > Use this file to discover all available pages before exploring further. # json > View Source on GitHub # module  pixeltable.functions.json Pixeltable UDFs for `JsonType`. Example: ```python theme={"theme":{"light":"light-plus","dark":"dark-plus"}} import pixeltable as pxt import pixeltable.functions as pxtf t = pxt.get_table(...) t.select(pxtf.json.make_list(t.json_col)).collect() ``` ## iterator  list\_iterator() ```python Signature theme={"theme":{"light":"light-plus","dark":"dark-plus"}} @pxt.iterator list_iterator( elements: pxt.Json[(Json, ...)] | None = None, *, mode: pxt.String = 'strict', **kwargs ) ``` Iterator over elements of a list or lists. There are two distinct call patterns: either a single positional argument; or one or more keyword arguments. * If a single positional argument is specified, as in `list_iterator(t.col)`, then the elements of `t.col` must contain lists of dictionaries with matching signatures (identical keys and compatible value types). The iterator will yield one new column for each key in the dictionaries, and one output row per element in the lists. * If multiple keyword arguments are specified, as in `list_iterator(val_1=t.col_1, val_2=t.col_2)`, then the elements of each input column must contain lists, but not necessarily lists of dictionaries. The iterator will yield one new column for each keyword argument, zipping together the individual lists. All of the inputs must be *typed* `Json` expressions. Untyped Json will be rejected (the type schema is necessary in order for Pixeltable to determine the types of the output columns). **Parameters:** * **`elements`** (`pxt.Json[(Json`): A list of dictionaries to iterate over. The dictionary keys will be used as column names in the output. Cannot be specified together with keyword arguments. * **`mode`** (`Any`): Only applies when called with keyword arguments. Determines how to handle lists of different lengths: * `'strict'`: Raises an error if the input lists have different lengths. * `'truncated'`: Iterates until the shortest input list is exhausted, ignoring any remaining elements in longer lists. * `'padded'`: Iterates until the longest input list is exhausted, yielding `None` for any missing elements from shorter lists. * **`**kwargs`** (`Any`): One or more lists to iterate over. The kwarg names will be used as column names in the output. Cannot be specified together with `elements`. ## uda  make\_list() ```python Signature theme={"theme":{"light":"light-plus","dark":"dark-plus"}} @pxt.uda make_list(*args, **kwargs) -> pxt.Json[(Json, ...)] ``` Collects arguments into a list. ## udf  concat() ```python Signature theme={"theme":{"light":"light-plus","dark":"dark-plus"}} @pxt.udf concat(self: pxt.Json | None, other: pxt.Json | None) -> pxt.Json ``` Concatenate two JSON arrays into a new array. Returns `null` if either operand is `null`. Raises if either operand is a non-null, non-array value. **Examples:** ```python theme={"theme":{"light":"light-plus","dark":"dark-plus"}} t.select(t.tags.concat(t.more_tags)).collect() ``` ## udf  contains() ```python Signature theme={"theme":{"light":"light-plus","dark":"dark-plus"}} @pxt.udf contains(self: pxt.Json, value: pxt.Json) -> pxt.Bool ``` Return `True` if `value` is an element of a JSON array or a key of a JSON object; `False` otherwise. **Examples:** ```python theme={"theme":{"light":"light-plus","dark":"dark-plus"}} t.where(t.detections.labels.contains('person')).collect() ``` ## udf  count() ```python Signature theme={"theme":{"light":"light-plus","dark":"dark-plus"}} @pxt.udf count(self: pxt.Json, value: pxt.Json) -> pxt.Int ``` Return the number of times `value` occurs in a JSON array. **Examples:** ```python theme={"theme":{"light":"light-plus","dark":"dark-plus"}} t.select(t.detections.labels.count('person')).collect() ``` ## udf  dumps() ```python Signature theme={"theme":{"light":"light-plus","dark":"dark-plus"}} @pxt.udf dumps(obj: pxt.Json) -> pxt.String ``` Serialize a JSON object to a string. Equivalent to [`json.dumps()`](https://docs.python.org/3/library/json.html#json.dumps). **Parameters:** * **`obj`** (`pxt.Json`): A JSON-serializable object (dict, list, or scalar). **Returns:** * `pxt.String`: A JSON-formatted string. ## udf  flatten() ```python Signature theme={"theme":{"light":"light-plus","dark":"dark-plus"}} @pxt.udf flatten(self: pxt.Json) -> pxt.Json ``` Concatenate the elements of a JSON array one level deep; non-array elements are kept as-is. **Examples:** ```python theme={"theme":{"light":"light-plus","dark":"dark-plus"}} t.select(t.chunks.flatten()).collect() ``` ## udf  get() ```python Signature theme={"theme":{"light":"light-plus","dark":"dark-plus"}} @pxt.udf get( self: pxt.Json | None, key: pxt.String, default: pxt.Json | None = None ) -> pxt.Json ``` Return the value of `key` if the value is a JSON object containing it, otherwise `default`. **Examples:** ```python theme={"theme":{"light":"light-plus","dark":"dark-plus"}} t.select(t.metadata.get('author', default='unknown')).collect() ``` ## udf  is\_empty() ```python Signature theme={"theme":{"light":"light-plus","dark":"dark-plus"}} @pxt.udf is_empty(self: pxt.Json | None) -> pxt.Bool ``` Return `True` if the value is `null`, an empty array, an empty object, or an empty string; `False` otherwise (including for numbers and booleans). **Examples:** ```python theme={"theme":{"light":"light-plus","dark":"dark-plus"}} t.where(~t.detections.bboxes.is_empty()).collect() ``` ## udf  items() ```python Signature theme={"theme":{"light":"light-plus","dark":"dark-plus"}} @pxt.udf items(self: pxt.Json) -> pxt.Json ``` Return the `[key, value]` pairs of a JSON object as a list. `keys()`, `values()`, and `items()` share the same ordering. **Examples:** ```python theme={"theme":{"light":"light-plus","dark":"dark-plus"}} t.select(t.metadata.items()).collect() ``` ## udf  keys() ```python Signature theme={"theme":{"light":"light-plus","dark":"dark-plus"}} @pxt.udf keys(self: pxt.Json) -> pxt.Json[(String, ...)] ``` Return the keys of a JSON object. `keys()`, `values()`, and `items()` share the same ordering. **Examples:** ```python theme={"theme":{"light":"light-plus","dark":"dark-plus"}} t.select(t.metadata.keys()).collect() ``` ## udf  len() ```python Signature theme={"theme":{"light":"light-plus","dark":"dark-plus"}} @pxt.udf len(self: pxt.Json) -> pxt.Int ``` Return the number of elements in a JSON array, keys in a JSON object, or characters in a JSON string. Not defined for numbers or booleans. A `null` value (or missing path) yields `null`. **Examples:** ```python theme={"theme":{"light":"light-plus","dark":"dark-plus"}} t.select(t.detections.bboxes.len()).collect() ``` ## udf  max() ```python Signature theme={"theme":{"light":"light-plus","dark":"dark-plus"}} @pxt.udf max(self: pxt.Json) -> pxt.Float | None ``` Return the largest number in a JSON array, or `null` if the array is empty. **Examples:** ```python theme={"theme":{"light":"light-plus","dark":"dark-plus"}} t.select(t.detections.scores.max()).collect() ``` ## udf  mean() ```python Signature theme={"theme":{"light":"light-plus","dark":"dark-plus"}} @pxt.udf mean(self: pxt.Json) -> pxt.Float | None ``` Return the arithmetic mean of the numbers in a JSON array, or `null` if the array is empty. **Examples:** ```python theme={"theme":{"light":"light-plus","dark":"dark-plus"}} t.select(t.detections.scores.mean()).collect() ``` ## udf  merge() ```python Signature theme={"theme":{"light":"light-plus","dark":"dark-plus"}} @pxt.udf merge(self: pxt.Json | None, other: pxt.Json | None) -> pxt.Json ``` Merge two JSON objects into a new object; on a key conflict the value from `other` wins. Returns `null` if either operand is `null`. Raises if either operand is a non-null, non-object value. **Examples:** ```python theme={"theme":{"light":"light-plus","dark":"dark-plus"}} t.select(t.defaults.merge(t.overrides)).collect() ``` ## udf  min() ```python Signature theme={"theme":{"light":"light-plus","dark":"dark-plus"}} @pxt.udf min(self: pxt.Json) -> pxt.Float | None ``` Return the smallest number in a JSON array, or `null` if the array is empty. **Examples:** ```python theme={"theme":{"light":"light-plus","dark":"dark-plus"}} t.select(t.detections.scores.min()).collect() ``` ## udf  sum() ```python Signature theme={"theme":{"light":"light-plus","dark":"dark-plus"}} @pxt.udf sum(self: pxt.Json) -> pxt.Float ``` Return the sum of the numbers in a JSON array (0 for an empty array). **Examples:** ```python theme={"theme":{"light":"light-plus","dark":"dark-plus"}} t.select(t.detections.scores.sum()).collect() ``` ## udf  values() ```python Signature theme={"theme":{"light":"light-plus","dark":"dark-plus"}} @pxt.udf values(self: pxt.Json) -> pxt.Json ``` Return the values of a JSON object. `keys()`, `values()`, and `items()` share the same ordering. **Examples:** ```python theme={"theme":{"light":"light-plus","dark":"dark-plus"}} t.select(t.metadata.values()).collect() ```