LinqExtensions (IQueryable & Polars LINQ)

Namespace: Polars.CSharp.Linq

Provides LINQ IQueryable extensions for C# Polars DataFrame and LazyFrame.

Properties & Indexers

Property	Type	Description
DefaultInspector	Action<string>	Gets or sets the default plan inspector action used when none is explicitly specified. Defaults to System.Console.WriteLine.

Constructors & Static Methods

AsAsyncEnumerable

Returns the input typed as IAsyncEnumerable for streaming async enumeration.

public static IAsyncEnumerable<T> AsAsyncEnumerable<T>(IQueryable<T> source)

Parameters

Name	Type	Description
source	IQueryable<T>	-

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AsEnumerable

Exposes a Series as a strongly-typed IEnumerable sequence of elements. For Struct Series, elements are materialized into objects matching the struct fields. For scalar Series, elements are materialized directly.

public static IEnumerable<T> AsEnumerable<T>(Series series)

Parameters

Name	Type	Description
series	Series	-

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AsPolarsQueryable

Convert DataReader to Polars Queryable

Transposes an in-memory sequence into a native Polars LazyFrame and exposes it as a Polars LINQ queryable.

public static IQueryable<T> AsPolarsQueryable<T>(IDataReader reader, int batchSize = 50000)
public static IQueryable<T> AsPolarsQueryable<T>(IEnumerable<T> source)

Parameters

Name	Type	Description
reader	IDataReader	-
batchSize	int	-
source	IEnumerable<T>	The in-memory collection

Returns: A queryable supported by the Polars native execution engine

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AsQueryable

Converts a LazyFrame into an IQueryable LINQ query provider. Operations will be translated to Polars Expressions and compiled into execution plans.

Converts an eager DataFrame into an IQueryable LINQ query provider backed by LazyFrame.

Converts a DataFrame into an IQueryable LINQ query provider, inferring the anonymous type or entity type directly from a sample sequence (e.g. source array).

Converts a LazyFrame into an IQueryable LINQ query provider, inferring the anonymous type or entity type directly from a sample sequence.

Converts a Series into an IQueryable LINQ query provider backed by Polars. For Struct Series, it is unnested into a multi-column DataFrame matching the struct fields. For scalar and other Series, it is converted into a single-column DataFrame.

Converts a Series into an IQueryable LINQ query provider, inferring the anonymous type or entity type directly from a sample sequence.

public static IQueryable<T> AsQueryable<T>(LazyFrame lf)
public static IQueryable<T> AsQueryable<T>(DataFrame df)
public static IQueryable<T> AsQueryable<T>(DataFrame df, IEnumerable<T> source)
public static IQueryable<T> AsQueryable<T>(LazyFrame lf, IEnumerable<T> source)
public static IQueryable<T> AsQueryable<T>(Series series)
public static IQueryable<T> AsQueryable<T>(Series series, IEnumerable<T> source)

Parameters

Name	Type	Description
lf	LazyFrame	-
df	DataFrame	The source DataFrame.
source	IEnumerable<T>	The source collection used solely for static type inference.
series	Series	-

Returns: A strongly-typed PolarsQuery provider.

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Average

Computes the average of the column.

Computes the average of the nullable column.

public static double Average<T>(T column)
public static double Average<T>(T? column)

Parameters

Name	Type	Description
column	T / T?	-

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Count

Counts the number of non-null values in the column.

Counts the number of non-null values in the nullable column.

public static int Count<T>(T column)
public static int Count<T>(T? column)
public static int Count(string? column)

Parameters

Name	Type	Description
column	T / T? / string?	-

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CumCount

Computes the cumulative count of the column.

public static long CumCount<T>(T? column, bool reverse = false)

Parameters

Name	Type	Description
column	T?	-
reverse	bool	-

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CumMax

Computes the cumulative maximum of the column.

public static T CumMax<T>(T? column, bool reverse = false)

Parameters

Name	Type	Description
column	T?	-
reverse	bool	-

---

CumMin

Computes the cumulative minimum of the column.

public static T CumMin<T>(T? column, bool reverse = false)

Parameters

Name	Type	Description
column	T?	-
reverse	bool	-

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CumProd

Computes the cumulative product of the column.

public static T CumProd<T>(T? column, bool reverse = false)

Parameters

Name	Type	Description
column	T?	-
reverse	bool	-

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CumSum

Computes the cumulative sum of the column.

public static T CumSum<T>(T? column, bool reverse = false)

Parameters

Name	Type	Description
column	T?	-
reverse	bool	-

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Diff

Computes the difference between the current value and the value n periods ago, with a specified null behavior.

public static T Diff<T>(T? column)
public static T Diff<T>(T? column, long n)
public static T Diff<T>(T? column, long n, NullBehavior nullBehavior)

Parameters

Name	Type	Description
column	T?	The column to compute differences for.
n	long	The number of periods to look back.
nullBehavior	NullBehavior	The behavior for handling null values.

Returns: The column with differences computed.

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Explain

Returns the Polars native query execution plan, including warnings if parts of the query fallback to managed client-side execution.

public static string Explain<T>(IQueryable<T> source, bool optimized = true)

Parameters

Name	Type	Description
source	IQueryable<T>	The source queryable.
optimized	bool	Whether to display the Polars optimized logical plan or the raw plan.

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InspectPlan

Inspects the query plan using the default inspector (Linq.LinqExtensions.DefaultInspector)

Inspects the query plan at the current pipeline stage and invokes a custom inspector action,

public static IQueryable<T> InspectPlan<T>(IQueryable<T> source, bool optimized = true)
public static IQueryable<T> InspectPlan<T>(IQueryable<T> source, Action<string> inspector, bool optimized = true)

Parameters

Name	Type	Description
source	IQueryable<T>	The source queryable.
optimized	bool	Whether to display the optimized plan. Defaults to true.
inspector	Action<string>	Action receiving the diagnostic plan string.

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Interpolate

Interpolates null values using the specified user-facing InterpolationMethod (defaults to Linear).

public static T Interpolate<T>(T? column, InterpolationMethod method = InterpolationMethod.Linear)

Parameters

Name	Type	Description
column	T?	-
method	InterpolationMethod	-

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InterpolateBy

Interpolates null values based on the values of another column (e.g., timestamps or indices).

public static T InterpolateBy<T, TBy>(T? column, TBy? byColumn)

Parameters

Name	Type	Description
column	T?	-
byColumn	TBy?	-

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Max

Finds the maximum value in the column.

Finds the maximum value in the nullable column.

Finds the maximum value in the string column.

public static T Max<T>(T column)
public static T? Max<T>(T? column)
public static string Max(string? column)

Parameters

Name	Type	Description
column	T / T? / string?	-

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Mean

Computes the mean of the column.

Computes the mean of the nullable column.

public static double Mean<T>(T? column)

Parameters

Name	Type	Description
column	T?	-

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Median

Computes the median value of the column.

public static double? Median<T>(T? column)

Parameters

Name	Type	Description
column	T?	-

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Min

Finds the minimum value in the column.

Finds the minimum value in the nullable column.

Finds the minimum value in the string column.

public static T Min<T>(T column)
public static T? Min<T>(T? column)
public static string Min(string? column)

Parameters

Name	Type	Description
column	T / T? / string?	-

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Over

Computes a windowed expression over a specified partition and order, with an optional descending order.

public static T Over<T, TPartition>(T? expr, TPartition? partitionBy)
public static T Over<T>(T? expr, params object[] partitionBy)
public static T Over<T, TPartition, TOrder>(
    T? expr,
    TPartition? partitionBy,
    TOrder? orderBy,
    bool descending = false
)

Parameters

Name	Type	Description
expr	T?	The expression to compute the windowed operation for.
partitionBy	TPartition? / object[]	The column(s) to partition by.
orderBy	TOrder?	The column(s) to order by.
descending	bool	Indicates whether to sort in descending order.

Returns: The column with the windowed expression computed.

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PctChange

Computes the percentage change between current and previous values.

public static double? PctChange<T>(T? column, long n = 1)

Parameters

Name	Type	Description
column	T?	-
n	long	-

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Quantile

Computes the quantile of the column with the specified probability and method.

public static double? Quantile<T>(T? column, double quantile, QuantileMethod method = QuantileMethod.Nearest)

Parameters

Name	Type	Description
column	T?	-
quantile	double	-
method	QuantileMethod	-

---

Rank

Computes the rank of values using the default Average method.

Computes the rank of values with a specified sorting order.

Computes the rank of values using user-facing RankMethod.

Computes the rank of values using user-facing RankMethod with seed.

public static double Rank<T>(T? column)
public static double Rank<T>(T? column, bool descending)
public static double Rank<T>(T? column, RankMethod method, bool descending = false)
public static double Rank<T>(
    T? column,
    RankMethod method,
    bool descending,
    ulong? seed
)

Parameters

Name	Type	Description
column	T?	-
descending	bool	-
method	RankMethod	-
seed	ulong?	-

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Shift

Shifts the values in a column by a specified offset, introducing nulls for the shifted positions.

public static T Shift<T>(T? column, long offset)
public static T Shift<T, TOffset>(T? column, TOffset? offsetColumn)

Parameters

Name	Type	Description
column	T?	The column to shift.
offset	long	The offset by which to shift the values.
offsetColumn	TOffset?	-

Returns: The shifted column.

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Std

Computes the sample standard deviation (ddof = 1 by default).

Computes sample standard deviation of a group by selector with default ddof = 1.

Computes standard deviation of a group by selector with explicit degree of freedom (ddof).

public static double Std<T>(T? column, byte ddof = 1)
public static double Std<TSource, TResult>(this IEnumerable<TSource> source, Expression<Func<TSource, TResult>> selector)
public static double Std<TSource, TResult>(this IEnumerable<TSource> source, Expression<Func<TSource, TResult>> selector, byte ddof)

Parameters

Name	Type	Description
column	T?	-
ddof	byte	-
source	IEnumerable<TSource>	-
selector	Expression<Func<TSource, TResult>>	-

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Sum

Computes the sum of the column.

Computes the sum of the nullable column.

public static T Sum<T>(T column)
public static T? Sum<T>(T? column)

Parameters

Name	Type	Description
column	T / T?	-

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ToArrayAsync

Asynchronously streams the query results and materializes them into an Array.

public static Task<T[]> ToArrayAsync<T>(IQueryable<T> source, CancellationToken cancellationToken = default)

Parameters

Name	Type	Description
source	IQueryable<T>	-
cancellationToken	CancellationToken	-

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ToDataFrame

Materializes an in-memory sequence of entities into an eager DataFrame. If the sequence is an IQueryable, native query execution and compilation is prioritized.

Compiles the LINQ query pipeline, executes Collect, and returns the resulting eager DataFrame.

public static DataFrame ToDataFrame<T>(IEnumerable<T> source)
public static DataFrame ToDataFrame<T>(IQueryable<T> query)

Parameters

Name	Type	Description
source	IEnumerable<T>	The sequence of elements.
query	IQueryable<T>	-

Returns: A new DataFrame containing the elements.

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ToDataFrameAsync

Asynchronously compiles and executes the query, materializing the result directly into a native Polars DataFrame.

Asynchronously drains an IAsyncEnumerable sequence of objects directly into a Polars DataFrame.

public static Task<DataFrame> ToDataFrameAsync<T>(IQueryable<T> source, Engine engine = Engine.Auto, CancellationToken cancellationToken = default)
public static Task<DataFrame> ToDataFrameAsync<T>(IAsyncEnumerable<T> source, CancellationToken cancellationToken = default)

Parameters

Name	Type	Description
source	IQueryable<T> / IAsyncEnumerable<T>	The source queryable.
engine	Engine	Execution engine selection (Auto, InMemory, Streaming, or Gpu).
cancellationToken	CancellationToken	Optional cooperative cancellation token.

Returns: A task yielding the resulting DataFrame.

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ToLazyFrame

Compiles the LINQ query pipeline and converts it back to a Polars LazyFrame.

Converts an in-memory sequence of entities into a LazyFrame. If the sequence is an IQueryable, native query execution and compilation is prioritized.

public static LazyFrame ToLazyFrame<T>(IQueryable<T> query)
public static LazyFrame ToLazyFrame<T>(IEnumerable<T> source)

Parameters

Name	Type	Description
query	IQueryable<T>	-
source	IEnumerable<T>	The sequence of elements.

Returns: A new LazyFrame containing the elements.

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ToListAsync

Asynchronously enumerates the query and materializes all results into a List.

public static Task<List<T>> ToListAsync<T>(IQueryable<T> source, CancellationToken cancellationToken = default)

Parameters

Name	Type	Description
source	IQueryable<T>	-
cancellationToken	CancellationToken	-

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ToLookup

Converts a queryable sequence into a PolarsLookup, grouping elements by a specified key selector and selecting elements with a specified selector.

public static PolarsLookup<TKey, TSource> ToLookup<TSource, TKey>(IQueryable<TSource> source, Expression<Func<TSource, TKey>> keySelector, IEqualityComparer<TKey>? comparer = null)
public static PolarsLookup<TKey, TElement> ToLookup<TSource, TKey, TElement>(
    IQueryable<TSource> source,
    Expression<Func<TSource, TKey>> keySelector,
    Expression<Func<TSource, TElement>> elementSelector,
    IEqualityComparer<TKey>? comparer = null
)

Parameters

Name	Type	Description
source	IQueryable<TSource>	The queryable sequence to convert.
keySelector	Expression<Func<TSource, TKey>>	The function to extract the key from each element.
comparer	IEqualityComparer<TKey>?	The equality comparer to use for the keys.
elementSelector	Expression<Func<TSource, TElement>>	The function to extract the element from each element.

Returns: The resulting PolarsLookup.

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ToSeries

Materializes an in-memory sequence of entities into a Polars Series. Object collections(non-scalar collections) will be converted into a Struct Series.

Compiles a LINQ query and materializes it into a Polars Series. If the query yields a single column, returns that column directly. If the query yields multiple columns, assembles them into a native Struct Series.

public static Series ToSeries<T>(IEnumerable<T> source, string name = "")
public static Series ToSeries<T>(IQueryable<T> query, string name = "")

Parameters

Name	Type	Description
source	IEnumerable<T>	The sequence or query of elements.
name	string	Optional name for the Series. Defaults to empty string.
query	IQueryable<T>	The query sequence.

Returns: A new Series containing the materialized values. / A new Series containing the query result.

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Var

Computes the sample variance (ddof = 1 by default).

Computes sample variance of a group by selector with default ddof = 1.

Computes variance of a group by selector with explicit degree of freedom (ddof).

public static double Var<T>(T? column, byte ddof = 1)
public static double Var<TSource, TResult>(this IEnumerable<TSource> source, Expression<Func<TSource, TResult>> selector)
public static double Var<TSource, TResult>(this IEnumerable<TSource> source, Expression<Func<TSource, TResult>> selector, byte ddof)

Parameters

Name	Type	Description
column	T?	-
ddof	byte	-
source	IEnumerable<TSource>	-
selector	Expression<Func<TSource, TResult>>	-

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