Replace infer_schema_length by infer_schema

[josevalim]

Today infer_schema_length has an awkward API, since setting it to nil is used to infer all columns and 0 is used to disable it.

I propose:

infer_schema: true | false | non_neg_integer()

Where true enables, false disables, and the integer configures the length. The default can be the same as today.

[cigrainger]

I like this, but what would we use for all rows? IIUC true -> default (1000 rows).

[josevalim]

true means all rows.

[lei0zhou]

thanks for improving this! just share a way duckdb did.
it has two parameters,

• auto_detect: true | false
• sample_size: BIGINT (-1, mean all rows, default 20480)

ref:
CSV Import – DuckDB
CSV Auto Detection – DuckDB

I am more than happy to take a stab at this

[ceyhunkerti]

Today infer_schema_length has an awkward API, since setting it to nil is used to infer all columns and 0 is used to disable it.

I propose:

infer_schema: true | false | non_neg_integer()

Where true enables, false disables, and the integer configures the length. The default can be the same as today.

• is it only for csv or should we also change it on load_ndjson ?
• Also one strange thing I didn't get is; polars side doesn't seem to have an option to disable schema inference for ndjson

👉🏼 given Option<NonZeroUsize>) to infer schema, what I understand is ;

• if it's None will use entire file
• else will use len(given) rows
• will fail at comptime if you give 0

    /// Set the JSON reader to infer the schema of the file. Currently, this is only used when reading from
    /// [`JsonFormat::JsonLines`], as [`JsonFormat::Json`] reads in the entire array anyway.
    ///
    /// When using [`JsonFormat::JsonLines`], `max_records = None` will read the entire buffer in order to infer the
    /// schema, `Some(1)` would look only at the first record, `Some(2)` the first two records, etc.
    ///
    /// It is an error to pass `max_records = Some(0)`, as a schema cannot be inferred from 0 records when deserializing
    /// from JSON (unlike CSVs, there is no header row to inspect for column names).
    pub fn infer_schema_len(mut self, max_records: Option<NonZeroUsize>) -> Self {
        self.infer_schema_len = max_records;
        self
    }