Polars.NET

Polars.NET brings the Polars data processing engine to the .NET ecosystem.

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1. QuickStart

using Polars.CSharp;
using static Polars.CSharp.Polars; // For Col(), Lit() helpers

// 1. Create a DataFrame
var data = new[] {
    new { Name = "Alice", Age = 25, Dept = "IT" },
    new { Name = "Bob", Age = 30, Dept = "HR" },
    new { Name = "Charlie", Age = 35, Dept = "IT" }
};
var df = DataFrame.From(data);

// 2. Filter & Aggregate
var res = df.
    Lazy()
    .Filter(Col("Age") > 28)
    .GroupBy("Dept")
    .Agg(
        Col("Age").Mean().Alias("AvgAge"),
        Col("Name").Count().Alias("Count")
    )
    .Sort("AvgAge");

// 3. Output
res.CollectStreaming().Show();
///shape: (2, 3)
/// ┌──────┬────────┬───────┐
/// │ Dept ┆ AvgAge ┆ Count │
/// │ ---  ┆ ---    ┆ ---   │
/// │ str  ┆ f64    ┆ u32   │
/// ╞══════╪════════╪═══════╡
/// │ HR   ┆ 30.0   ┆ 1     │
/// │ IT   ┆ 35.0   ┆ 1     │
/// └──────┴────────┴───────┘

2.F# Support

let windowDf = 
    df
    |> pl.select [
        pl.col "Date"
        pl.col "City"
        pl.col "Temperature"
        
        // Over(Date): Calculate mean value by group
        (pl.col("Temperature").Mean().Over(pl.col "Date"))
            .Alias "Daily_Avg"
            
        (pl.col "Temperature" - pl.col("Temperature").Mean().Over(pl.col "Date"))
            .Alias "Diff"
    ]
    |> pl.sort (pl.col "Date", false)

windowDf.Show()
/// result
/// shape: (3, 5)
/// ┌────────────┬────────────┬─────────────┬───────────┬───────┐
/// │ Date       ┆ City       ┆ Temperature ┆ Daily_Avg ┆ Diff  │
/// │ ---        ┆ ---        ┆ ---         ┆ ---       ┆ ---   │
/// │ date       ┆ str        ┆ f64         ┆ f64       ┆ f64   │
/// ╞════════════╪════════════╪═════════════╪═══════════╪═══════╡
/// │ 2023-01-01 ┆ London     ┆ 10.5        ┆ 9.75      ┆ 0.75  │
/// │ 2023-01-01 ┆ Manchester ┆ 9.0         ┆ 9.75      ┆ -0.75 │
/// │ 2023-01-02 ┆ London     ┆ 12.1        ┆ 12.1      ┆ 0.0   │
/// └────────────┴────────────┴─────────────┴───────────┴───────┘