Method: Polars::Functions#approx_n_unique

Defined in:
lib/polars/functions/lazy.rb

#approx_n_unique(*columns) ⇒ Expr

Approximate count of unique values.

This function is syntactic sugar for col(columns).approx_n_unique, and uses the HyperLogLog++ algorithm for cardinality estimation.

Examples:

df = Polars::DataFrame.new(
  {
    "a" => [1, 8, 1],
    "b" => [4, 5, 2],
    "c" => ["foo", "bar", "foo"]
  }
)
df.select(Polars.approx_n_unique("a"))
# =>
# shape: (1, 1)
# ┌─────┐
# │ a   │
# │ --- │
# │ u32 │
# ╞═════╡
# │ 2   │
# └─────┘
df.select(Polars.approx_n_unique("b", "c"))
# =>
# shape: (1, 2)
# ┌─────┬─────┐
# │ b   ┆ c   │
# │ --- ┆ --- │
# │ u32 ┆ u32 │
# ╞═════╪═════╡
# │ 3   ┆ 2   │
# └─────┴─────┘

Parameters:

  • columns (Array) —

    One or more column names.

Returns:


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# File 'lib/polars/functions/lazy.rb', line 403

def approx_n_unique(*columns)
  col(*columns).approx_n_unique
end