Struct polars_lazy::frame::LazyGroupBy

pub struct LazyGroupBy { /* fields omitted */ }

This is supported on crate feature compile only.

Utility struct for lazy groupby operation.

Implementations

impl LazyGroupBy

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

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::*;

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

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> + 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.