Struct polars::frame::group_by::GroupBy

pub struct GroupBy<'df, 'selection_str> { /* fields omitted */ }

Returned by a groupby operation on a DataFrame. This struct supports several aggregations.

Until described otherwise, the examples in this struct are performed on the following DataFrame:

use polars::prelude::*;

let dates = &[
"2020-08-21",
"2020-08-21",
"2020-08-22",
"2020-08-23",
"2020-08-22",
];
// date format
let fmt = "%Y-%m-%d";
// create date series
let s0 = Date32Chunked::parse_from_str_slice("date", dates, fmt)
        .into_series();
// create temperature series
let s1 = Series::new("temp", [20, 10, 7, 9, 1].as_ref());
// create rain series
let s2 = Series::new("rain", [0.2, 0.1, 0.3, 0.1, 0.01].as_ref());
// create a new DataFrame
let df = DataFrame::new(vec![s0, s1, s2]).unwrap();
println!("{:?}", df);

Outputs:

+------------+------+------+
| date       | temp | rain |
| ---        | ---  | ---  |
| date32     | i32  | f64  |
+============+======+======+
| 2020-08-21 | 20   | 0.2  |
+------------+------+------+
| 2020-08-21 | 10   | 0.1  |
+------------+------+------+
| 2020-08-22 | 7    | 0.3  |
+------------+------+------+
| 2020-08-23 | 9    | 0.1  |
+------------+------+------+
| 2020-08-22 | 1    | 0.01 |
+------------+------+------+

Implementations

impl<'df, 'selection_str> GroupBy<'df, 'selection_str>

pub fn select<S, J>(self, selection: S) -> Self where
    S: Selection<'selection_str, J>, 

Select the column by which the determine the groups. You can select a single column or a slice of columns.

pub fn mean(&self) -> Result<DataFrame>

Aggregate grouped series and compute the mean per group.

Example

fn example(df: DataFrame) -> Result<DataFrame> {
    df.groupby("date")?.select(&["temp", "rain"]).mean()
}

Returns:

+------------+-----------+-----------+
| date       | temp_mean | rain_mean |
| ---        | ---       | ---       |
| date32     | f64       | f64       |
+============+===========+===========+
| 2020-08-23 | 9         | 0.1       |
+------------+-----------+-----------+
| 2020-08-22 | 4         | 0.155     |
+------------+-----------+-----------+
| 2020-08-21 | 15        | 0.15      |
+------------+-----------+-----------+

pub fn sum(&self) -> Result<DataFrame>

Aggregate grouped series and compute the sum per group.

Example

fn example(df: DataFrame) -> Result<DataFrame> {
    df.groupby("date")?.select("temp").sum()
}

Returns:

+------------+----------+
| date       | temp_sum |
| ---        | ---      |
| date32     | i32      |
+============+==========+
| 2020-08-23 | 9        |
+------------+----------+
| 2020-08-22 | 8        |
+------------+----------+
| 2020-08-21 | 30       |
+------------+----------+

pub fn min(&self) -> Result<DataFrame>

Aggregate grouped series and compute the minimal value per group.

Example

fn example(df: DataFrame) -> Result<DataFrame> {
    df.groupby("date")?.select("temp").min()
}

Returns:

+------------+----------+
| date       | temp_min |
| ---        | ---      |
| date32     | i32      |
+============+==========+
| 2020-08-23 | 9        |
+------------+----------+
| 2020-08-22 | 1        |
+------------+----------+
| 2020-08-21 | 10       |
+------------+----------+

pub fn max(&self) -> Result<DataFrame>

Aggregate grouped series and compute the maximum value per group.

Example

fn example(df: DataFrame) -> Result<DataFrame> {
    df.groupby("date")?.select("temp").max()
}

Returns:

+------------+----------+
| date       | temp_max |
| ---        | ---      |
| date32     | i32      |
+============+==========+
| 2020-08-23 | 9        |
+------------+----------+
| 2020-08-22 | 7        |
+------------+----------+
| 2020-08-21 | 20       |
+------------+----------+

pub fn first(&self) -> Result<DataFrame>

Aggregate grouped Series and find the first value per group.

Example

fn example(df: DataFrame) -> Result<DataFrame> {
    df.groupby("date")?.select("temp").first()
}

Returns:

+------------+------------+
| date       | temp_first |
| ---        | ---        |
| date32     | i32        |
+============+============+
| 2020-08-23 | 9          |
+------------+------------+
| 2020-08-22 | 7          |
+------------+------------+
| 2020-08-21 | 20         |
+------------+------------+

pub fn last(&self) -> Result<DataFrame>

Aggregate grouped Series and return the last value per group.

Example

fn example(df: DataFrame) -> Result<DataFrame> {
    df.groupby("date")?.select("temp").last()
}

Returns:

+------------+------------+
| date       | temp_last |
| ---        | ---        |
| date32     | i32        |
+============+============+
| 2020-08-23 | 9          |
+------------+------------+
| 2020-08-22 | 1          |
+------------+------------+
| 2020-08-21 | 10         |
+------------+------------+

pub fn n_unique(&self) -> Result<DataFrame>

Aggregate grouped Series by counting the number of unique values.

Example

fn example(df: DataFrame) -> Result<DataFrame> {
    df.groupby("date")?.select("temp").n_unique()
}

Returns:

+------------+---------------+
| date       | temp_n_unique |
| ---        | ---           |
| date32     | u32           |
+============+===============+
| 2020-08-23 | 1             |
+------------+---------------+
| 2020-08-22 | 2             |
+------------+---------------+
| 2020-08-21 | 2             |
+------------+---------------+

pub fn quantile(&self, quantile: f64) -> Result<DataFrame>

Aggregate grouped Series and determine the quantile per group.

Example

fn example(df: DataFrame) -> Result<DataFrame> {
    df.groupby("date")?.select("temp").quantile(0.2)
}

pub fn median(&self) -> Result<DataFrame>

Aggregate grouped Series and determine the median per group.

Example

fn example(df: DataFrame) -> Result<DataFrame> {
    df.groupby("date")?.select("temp").median()
}

pub fn count(&self) -> Result<DataFrame>

Aggregate grouped series and compute the number of values per group.

Example

fn example(df: DataFrame) -> Result<DataFrame> {
    df.groupby("date")?.select("temp").count()
}

Returns:

+------------+------------+
| date       | temp_count |
| ---        | ---        |
| date32     | u32        |
+============+============+
| 2020-08-23 | 1          |
+------------+------------+
| 2020-08-22 | 2          |
+------------+------------+
| 2020-08-21 | 2          |
+------------+------------+

pub fn groups(&self) -> Result<DataFrame>

Get the groupby group indexes.

Example

fn example(df: DataFrame) -> Result<DataFrame> {
    df.groupby("date")?.groups()
}

Returns:

+--------------+------------+
| date         | groups     |
| ---          | ---        |
| date32(days) | list [u32] |
+==============+============+
| 2020-08-23   | "[3]"      |
+--------------+------------+
| 2020-08-22   | "[2, 4]"   |
+--------------+------------+
| 2020-08-21   | "[0, 1]"   |
+--------------+------------+

pub fn agg<Column, S, Slice>(
    &self,
    column_to_agg: &[(Column, Slice)]
) -> Result<DataFrame> where
    S: AsRef<str>,
    S: AsRef<str>,
    Slice: AsRef<[S]>,
    Column: AsRef<str>, 

Combine different aggregations on columns

Operations

• count
• first
• last
• sum
• min
• max
• mean
• median

Example

fn example(df: DataFrame) -> Result<DataFrame> {
    df.groupby("date")?.agg(&[("temp", &["n_unique", "sum", "min"])])
}

Returns:

+--------------+---------------+----------+----------+
| date         | temp_n_unique | temp_sum | temp_min |
| ---          | ---           | ---      | ---      |
| date32(days) | u32           | i32      | i32      |
+==============+===============+==========+==========+
| 2020-08-23   | 1             | 9        | 9        |
+--------------+---------------+----------+----------+
| 2020-08-22   | 2             | 8        | 1        |
+--------------+---------------+----------+----------+
| 2020-08-21   | 2             | 30       | 10       |
+--------------+---------------+----------+----------+

pub fn agg_list(&self) -> Result<DataFrame>

Aggregate the groups of the groupby operation into lists.

Example

fn example(df: DataFrame) -> Result<DataFrame> {
    // GroupBy and aggregate to Lists
    df.groupby("date")?.select("temp").agg_list()
}

Returns:

+------------+------------------------+
| date       | temp_agg_list          |
| ---        | ---                    |
| date32     | list [i32]             |
+============+========================+
| 2020-08-23 | "[Some(9)]"            |
+------------+------------------------+
| 2020-08-22 | "[Some(7), Some(1)]"   |
+------------+------------------------+
| 2020-08-21 | "[Some(20), Some(10)]" |
+------------+------------------------+

pub fn pivot(
    &mut self,
    pivot_column: &'selection_str str,
    values_column: &'selection_str str
) -> Pivot<'_, '_>

Pivot a column of the current DataFrame and perform one of the following aggregations:

• first
• sum
• min
• max
• mean
• median

The pivot operation consists of a group by one, or multiple collumns (these will be the new y-axis), column that will be pivoted (this will be the new x-axis) and an aggregation.

Panics

If the values column is not a numerical type, the code will panic.

Example

use polars::prelude::*;
let s0 = Series::new("foo", ["A", "A", "B", "B", "C"].as_ref());
let s1 = Series::new("N", [1, 2, 2, 4, 2].as_ref());
let s2 = Series::new("bar", ["k", "l", "m", "n", "o"].as_ref());
// create a new DataFrame
let df = DataFrame::new(vec![s0, s1, s2]).unwrap();

fn example(df: DataFrame) -> Result<DataFrame> {
    df.groupby("foo")?
    .pivot("bar", "N")
    .first()
}

Transforms:

+-----+-----+-----+
| foo | N   | bar |
| --- | --- | --- |
| str | i32 | str |
+=====+=====+=====+
| "A" | 1   | "k" |
+-----+-----+-----+
| "A" | 2   | "l" |
+-----+-----+-----+
| "B" | 2   | "m" |
+-----+-----+-----+
| "B" | 4   | "n" |
+-----+-----+-----+
| "C" | 2   | "o" |
+-----+-----+-----+

Into:

+-----+------+------+------+------+------+
| foo | o    | n    | m    | l    | k    |
| --- | ---  | ---  | ---  | ---  | ---  |
| str | i32  | i32  | i32  | i32  | i32  |
+=====+======+======+======+======+======+
| "A" | null | null | null | 2    | 1    |
+-----+------+------+------+------+------+
| "B" | null | 4    | 2    | null | null |
+-----+------+------+------+------+------+
| "C" | 2    | null | null | null | null |
+-----+------+------+------+------+------+

Trait Implementations

impl<'df, 'selection_str> Clone for GroupBy<'df, 'selection_str>

fn clone(&self) -> GroupBy<'df, 'selection_str>

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl<'df, 'selection_str> Debug for GroupBy<'df, 'selection_str>

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.