polars.Expr.str.json_decode#

Expr.str.json_decode( dtype: PolarsDataType | DataTypeExpr, *, infer_schema_length: int | None = None, ) → Expr[source]#

Parse string values as JSON.

Throws an error if invalid JSON strings are encountered.

Parameters:

dtype: The dtype to cast the extracted value to.
infer_schema_length: Deprecated and ignored.

Changed in version 1.33.0: Deprecate infer_schema_length and make dtype non-optional to ensure that the planner can determine the output datatype.

See also

json_path_match: Extract the first match from a JSON string using the provided JSONPath.

Examples

>>> df = pl.DataFrame(
...     {"json": ['{"a":1, "b": true}', None, '{"a":2, "b": false}']}
... )
>>> dtype = pl.Struct([pl.Field("a", pl.Int64), pl.Field("b", pl.Boolean)])
>>> df.with_columns(decoded=pl.col("json").str.json_decode(dtype))
shape: (3, 2)
┌─────────────────────┬───────────┐
│ json                ┆ decoded   │
│ ---                 ┆ ---       │
│ str                 ┆ struct[2] │
╞═════════════════════╪═══════════╡
│ {"a":1, "b": true}  ┆ {1,true}  │
│ null                ┆ null      │
│ {"a":2, "b": false} ┆ {2,false} │
└─────────────────────┴───────────┘