Serialize Polars `dataframe` to `serde_json::Value`

Question

In Polars, it is simple enough to serialize a DataFrame to a json string: JsonWriter::new(dest).finish(&df)?.

Is it possible to serialize to a json Value — a serde_json::Value — that is the Value::Array of records? Obviously, I could write the json to an in-memory string, then deserialize it into a serde_json::Value. But I'm wondering if there is a direct path from DataFrame to serde_json::Value.

This would be the rough equivalent of pandas df.to_dict(orient="records").

Answer 1

You need to add the serde feature.

cargo add polars --features serde

use polars::prelude::*;

fn main() {
    let df = df! {
        "a" => [1,2,3,4,5],
    }
    .unwrap();
    let df_json = serde_json::to_value(&df).unwrap();
    println!("df_json {df_json}");
}

Note, Polars implements a custom de/serialize, and it may not align with the pandas equivalent mentioned.

The JSON result from above:

{
  "columns": [
    {
      "datatype": "Int32",
      "name": "a",
      "values": [1,2,3,4,5]
    }
  ]
}