Struct polars::prelude::LazyGroupBy

pub struct LazyGroupBy { /* private fields */ }

Utility struct for lazy groupby operation.

Implementations

impl LazyGroupBy

pub fn agg<E>(self, aggs: E) -> LazyFrame where
    E: AsRef<[Expr]>, 

Group by and aggregate.

Select a column with col and choose an aggregation. If you want to aggregate all columns use col("*").

Example

use polars_core::prelude::*;
use polars_lazy::prelude::*;
use polars_arrow::prelude::QuantileInterpolOptions;

fn example(df: DataFrame) -> LazyFrame {
      df.lazy()
       .groupby_stable([col("date")])
       .agg([
           col("rain").min(),
           col("rain").sum(),
           col("rain").quantile(0.5, QuantileInterpolOptions::Nearest).alias("median_rain"),
       ])
}

pub fn head(self, n: Option<usize>) -> LazyFrame

Return first n rows of each group

pub fn tail(self, n: Option<usize>) -> LazyFrame

Return last n rows of each group

pub fn apply<F>(self, f: F) -> LazyFrame where
    F: 'static + Fn(DataFrame) -> Result<DataFrame, PolarsError> + Send + Sync, 

Apply a function over the groups as a new DataFrame. It is not recommended that you use this as materializing the DataFrame is quite expensive.