Polars library

The polars are built-in adaptors that can be used to perform data manipulation and transformation on dataframes. Polars adaptor is enabled for operators that can access dataframe states and you don't need to add any flag in your operator definition.

The polars rust api can be used when dataframe state is available. For example, following snippet show performing polar operator on state that return dataframe. Please refer to states states section for more details.

In here, count_per_word is a state that returns a dataframe and assign to variable df. Then any dataframe operation can be performed on df variable.

- operator: map
  run: |
    fn map_words_to_occurrence(key: String) -> Result<String, String> {
        use polars::prelude::{col,lit,IntoLazy};

        let df = count_per_word();
        let val = df
            .clone()
            .lazy()
            .filter(col("id").eq(lit(key.clone())))
            .collect()
            .expect("parse");
        println!("{:#?}", val);

        if let Some(count) = val.column("occurrences").unwrap().i32().unwrap().get(0) {
            Ok(format!("key: {} count: {}",key,count))
        } else {
            Ok(format!("key: {} not found",key))
        }
    }