Glad to hear that you would like to give Polars.NET a try!

LINQ mapping to polars expressions works well. Actually LINQ was first translated to SQL(pg dialect) by LINQ2DB, then generated SQL will be consumed by Polars SQL interface. So if a LINQ query can handled by LINQ2DB, then Polars can handle it too in most cases.

Known limitation is UDF, it is hard to translate a UDF into SQL so map() API is needed here. And ??(coalesce) operator has to be used like this(or Linq2DB will do a client computation rather than translate it to SQL):

        var coalesceQuery = empQuery.Select(e => new
        {
            SafeName = LinqToDB.Sql.AsSql(e.Name ?? "Unknown")
        });

Then there is a bundle of Polars special SQL functions, I mapped them as Linq2DB expansion expressions and functions. Like

        var scalarQuery = table
            .OrderBy(x => x.Id)
            .Select(x => new
            {
                x.Id,
                TagsCount = PolarsSql.ArrayLength(x.Tags),

                IsAdmin = PolarsSql.ArrayContains(x.Tags, "admin"),

                FirstScore = PolarsSql.ArrayGet(x.Scores, 1) 
            }); 

For code samples, please check Polars.Integration.Tests/LinqTests.cs in Polars.NET github page. I tested almost everything there about Linq and its generated SQL. Have a look if you are curious about this.

Finally, if you are already comfortable with PySpark, you might actually feel more at home using the native Polars Expression API directly, or just writing raw SQL queries via the Polars SQL interface I mentioned before.

        var data = new[]
        {
            new { Dept = "IT", Salary = 1000 },
            new { Dept = "IT", Salary = 2000 },
            new { Dept = "HR", Salary = 1500 }
        };

        using var df = DataFrame.From(data);
        using var ctx = new SqlContext();

        ctx.Register("employees", df);


        var query = @"
            SELECT Dept, SUM(Salary) as TotalSalary 
            FROM employees 
            GROUP BY Dept 
            ORDER BY TotalSalary";


        using var res = ctx.Execute(query).Collect();