polars_lazy

Module dsl

Source
Expand description

Domain specific language for the Lazy API.

This DSL revolves around the Expr type, which represents an abstract operation on a DataFrame, such as mapping over a column, filtering, group_by, or aggregation. In general, functions on LazyFrames consume the LazyFrame and produce a new LazyFrame representing the result of applying the function and passed expressions to the consumed LazyFrame. At runtime, when LazyFrame::collect is called, the expressions that comprise the LazyFrame’s logical plan are materialized on the actual underlying Series. For instance, let expr = col("x").pow(lit(2)).alias("x2"); would produce an expression representing the abstract operation of squaring the column "x" and naming the resulting column "x2", and to apply this operation to a LazyFrame, you’d use let lazy_df = lazy_df.with_column(expr);. (Of course, a column named "x" must either exist in the original DataFrame or be produced by one of the preceding operations on the LazyFrame.)

There are many, many free functions that this module exports that produce an Expr from scratch; col and lit are two examples. Expressions also have several methods, such as pow and alias, that consume them and produce a new expression.

Several expressions are only available when the necessary feature is enabled. Examples of features that unlock specialized expression include string, temporal, and dtype-categorical. These specialized expressions provide implementations of functions that you’d otherwise have to implement by hand.

Because of how abstract and flexible the Expr type is, care must be take to ensure you only attempt to perform sensible operations with them. For instance, as mentioned above, you have to make sure any columns you reference already exist in the LazyFrame. Furthermore, there is nothing stopping you from calling, for example, any with an expression that will yield an f64 column (instead of bool), or col("string") - col("f64"), which would attempt to subtract an f64 Series from a string Series. These kinds of invalid operations will only yield an error at runtime, when collect is called on the LazyFrame.

Re-exports§

Modules§

Structs§

Enums§

Traits§

Functions§

  • all
    Selects all columns. Shorthand for col("*").
  • all_horizontal
    Create a new column with the bitwise-and of the elements in each row.
  • any_horizontal
    Create a new column with the bitwise-or of the elements in each row.
  • apply_binary
    Like map_binary, but used in a group_by-aggregation context.
  • apply_multiple
    Apply a function/closure over the groups of multiple columns. This should only be used in a group_by aggregation.
  • arange
    Generate a range of integers.
  • arg_sort_byrange
    Find the indexes that would sort these series in order of appearance.
  • arg_wherearg_where
    Get the indices where condition evaluates true.
  • as_struct
    Take several expressions and collect them into a StructChunked.
  • avg
    Find the mean of all the values in the column named name. Alias for mean.
  • binary_expr
    Compute op(l, r) (or equivalently l op r). l and r must have types compatible with the Operator.
  • cast
    Casts the column given by Expr to a different type.
  • coalesce
    Folds the expressions from left to right keeping the first non-null values.
  • col
    Create a Column Expression based on a column name.
  • cols
    Select multiple columns by name.
  • concat_expr
  • concat_list
    Concat lists entries.
  • concat_strconcat_str and strings
    Horizontally concat string columns in linear time
  • cov
    Compute the covariance between two columns.
  • cum_fold_exprsdtype-struct
    Accumulate over multiple columns horizontally / row wise.
  • cum_reduce_exprsdtype-struct
    Accumulate over multiple columns horizontally / row wise.
  • date_rangestemporal
    Create a column of date ranges from a start and stop expression.
  • datetime
    Construct a column of Datetime from the provided DatetimeArgs.
  • datetime_rangedtype-datetime
    Create a datetime range from a start and stop expression.
  • datetime_rangesdtype-datetime
    Create a column of datetime ranges from a start and stop expression.
  • dtype_col
    Select multiple columns by dtype.
  • dtype_cols
    Select multiple columns by dtype.
  • duration
    Construct a column of Duration from the provided DurationArgs
  • first
    First column in a DataFrame.
  • fold_exprs
    Accumulate over multiple columns horizontally / row wise.
  • format_strconcat_str and strings
    Format the results of an array of expressions using a format string
  • index_cols
    Select multiple columns by index.
  • int_range
    Generate a range of integers.
  • int_ranges
    Generate a range of integers for each row of the input columns.
  • is_not_null
    A column which is false wherever expr is null, true elsewhere.
  • is_null
    A column which is true wherever expr is null, false elsewhere.
  • last
    Last column in a DataFrame.
  • len
    Return the number of rows in the context.
  • lit
    Create a Literal Expression from L. A literal expression behaves like a column that contains a single distinct value.
  • map_binary
    Apply a closure on the two columns that are evaluated from Expr a and Expr b.
  • map_list_multiple
    Apply a function/closure over multiple columns once the logical plan get executed.
  • map_multiple
    Apply a function/closure over multiple columns once the logical plan get executed.
  • max
    Find the maximum of all the values in the column named name. Shorthand for col(name).max().
  • max_horizontal
    Create a new column with the maximum value per row.
  • mean
    Find the mean of all the values in the column named name. Shorthand for col(name).mean().
  • mean_horizontal
    Compute the mean of all values horizontally across columns.
  • median
    Find the median of all the values in the column named name. Shorthand for col(name).median().
  • min
    Find the minimum of all the values in the column named name. Shorthand for col(name).min().
  • min_horizontal
    Create a new column with the minimum value per row.
  • not
    Negates a boolean column.
  • nth
    Nth column in a DataFrame.
  • pearson_corr
    Compute the pearson correlation between two columns.
  • quantile
    Find a specific quantile of all the values in the column named name.
  • reduce_exprs
    Analogous to Iterator::reduce.
  • repeat
    Create a column of length n containing n copies of the literal value.
  • rolling_corrrolling_window and cov
  • rolling_covrolling_window and cov
  • spearman_rank_corrrank and propagate_nans
    Compute the spearman rank correlation between two columns. Missing data will be excluded from the computation.
  • sum
    Sum all the values in the column named name. Shorthand for col(name).sum().
  • sum_horizontal
    Sum all values horizontally across columns.
  • ternary_expr
  • time_rangesdtype-time
    Create a column of time ranges from a start and stop expression.
  • when
    Start a when-then-otherwise expression.

Type Aliases§