Method: Polars::Expr#replace_strict

Defined in:

lib/polars/expr.rb

#replace_strict(old, new = NO_DEFAULT, default: NO_DEFAULT, return_dtype: nil) ⇒ Expr

Note:

The global string cache must be enabled when replacing categorical values.

Replace all values by different values.

Examples:

Replace values by passing arrays to the old and new parameters.

df = Polars::DataFrame.new({"a" => [1, 2, 2, 3]})
df.with_columns(
  replaced: Polars.col("a").replace_strict([1, 2, 3], [100, 200, 300])
)
# =>
# shape: (4, 2)
# ┌─────┬──────────┐
# │ a   ┆ replaced │
# │ --- ┆ ---      │
# │ i64 ┆ i64      │
# ╞═════╪══════════╡
# │ 1   ┆ 100      │
# │ 2   ┆ 200      │
# │ 2   ┆ 200      │
# │ 3   ┆ 300      │
# └─────┴──────────┘

By default, an error is raised if any non-null values were not replaced. Specify a default to set all values that were not matched.

mapping = {2 => 200, 3 => 300}
df.with_columns(replaced: Polars.col("a").replace_strict(mapping, default: -1))
# =>
# shape: (4, 2)
# ┌─────┬──────────┐
# │ a   ┆ replaced │
# │ --- ┆ ---      │
# │ i64 ┆ i64      │
# ╞═════╪══════════╡
# │ 1   ┆ -1       │
# │ 2   ┆ 200      │
# │ 2   ┆ 200      │
# │ 3   ┆ 300      │
# └─────┴──────────┘

Replacing by values of a different data type sets the return type based on a combination of the new data type and the default data type.

df = Polars::DataFrame.new({"a" => ["x", "y", "z"]})
mapping = {"x" => 1, "y" => 2, "z" => 3}
df.with_columns(replaced: Polars.col("a").replace_strict(mapping))
# =>
# shape: (3, 2)
# ┌─────┬──────────┐
# │ a   ┆ replaced │
# │ --- ┆ ---      │
# │ str ┆ i64      │
# ╞═════╪══════════╡
# │ x   ┆ 1        │
# │ y   ┆ 2        │
# │ z   ┆ 3        │
# └─────┴──────────┘

df.with_columns(replaced: Polars.col("a").replace_strict(mapping, default: "x"))
# =>
# shape: (3, 2)
# ┌─────┬──────────┐
# │ a   ┆ replaced │
# │ --- ┆ ---      │
# │ str ┆ str      │
# ╞═════╪══════════╡
# │ x   ┆ 1        │
# │ y   ┆ 2        │
# │ z   ┆ 3        │
# └─────┴──────────┘

Set the return_dtype parameter to control the resulting data type directly.

df.with_columns(
  replaced: Polars.col("a").replace_strict(mapping, return_dtype: Polars::UInt8)
)
# =>
# shape: (3, 2)
# ┌─────┬──────────┐
# │ a   ┆ replaced │
# │ --- ┆ ---      │
# │ str ┆ u8       │
# ╞═════╪══════════╡
# │ x   ┆ 1        │
# │ y   ┆ 2        │
# │ z   ┆ 3        │
# └─────┴──────────┘

Expression input is supported for all parameters.

df = Polars::DataFrame.new({"a" => [1, 2, 2, 3], "b" => [1.5, 2.5, 5.0, 1.0]})
df.with_columns(
  replaced: Polars.col("a").replace_strict(
    Polars.col("a").max,
    Polars.col("b").sum,
    default: Polars.col("b")
  )
)
# =>
# shape: (4, 3)
# ┌─────┬─────┬──────────┐
# │ a   ┆ b   ┆ replaced │
# │ --- ┆ --- ┆ ---      │
# │ i64 ┆ f64 ┆ f64      │
# ╞═════╪═════╪══════════╡
# │ 1   ┆ 1.5 ┆ 1.5      │
# │ 2   ┆ 2.5 ┆ 2.5      │
# │ 2   ┆ 5.0 ┆ 5.0      │
# │ 3   ┆ 1.0 ┆ 10.0     │
# └─────┴─────┴──────────┘

Parameters:

• old (Object) —

  Value or array of values to replace. Accepts expression input. Arrays are parsed as Series, other non-expression inputs are parsed as literals. Also accepts a mapping of values to their replacement as syntactic sugar for replace_all(old: Series.new(mapping.keys), new: Series.new(mapping.values)).

• new (Object) (defaults to: NO_DEFAULT) —

  Value or array of values to replace by. Accepts expression input. Arrays are parsed as Series, other non-expression inputs are parsed as literals. Length must match the length of old or have length 1.

• default (Object) (defaults to: NO_DEFAULT) —

  Set values that were not replaced to this value. If no default is specified, (default), an error is raised if any values were not replaced. Accepts expression input. Non-expression inputs are parsed as literals.

• return_dtype (Object) (defaults to: nil) —

  The data type of the resulting expression. If set to nil (default), the data type is determined automatically based on the other inputs.

Returns:

• (Expr)

# File 'lib/polars/expr.rb', line 8106

def replace_strict(
  old,
  new = NO_DEFAULT,
  default: NO_DEFAULT,
  return_dtype: nil
)
  if new.eql?(NO_DEFAULT) && old.is_a?(Hash)
    new = Series.new(old.values)
    old = Series.new(old.keys)
  end

  old = Utils.parse_into_expression(old, str_as_lit: true, list_as_series: true)
  new = Utils.parse_into_expression(new, str_as_lit: true, list_as_series: true)

  default = default.eql?(NO_DEFAULT) ? nil : Utils.parse_into_expression(default, str_as_lit: true)

  wrap_expr(
    _rbexpr.replace_strict(old, new, default, return_dtype)
  )
end