Method: Polars::Functions#count

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

#count(*columns) ⇒ Expr

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

This function is syntactic sugar for col(columns).count.

Calling this function without any arguments returns the number of rows in the context. This way of using the function is deprecated. Please use len instead.

Examples:

df = Polars::DataFrame.new(
  {
    "a" => [1, 2, nil],
    "b" => [3, nil, nil],
    "c" => ["foo", "bar", "foo"]
  }
)
df.select(Polars.count("a"))
# =>
# shape: (1, 1)
# ┌─────┐
# │ a   │
# │ --- │
# │ u32 │
# ╞═════╡
# │ 2   │
# └─────┘

Return the number of non-null values in multiple columns.

df.select(Polars.count("b", "c"))
# =>
# shape: (1, 2)
# ┌─────┬─────┐
# │ b   ┆ c   │
# │ --- ┆ --- │
# │ u32 ┆ u32 │
# ╞═════╪═════╡
# │ 1   ┆ 3   │
# └─────┴─────┘

Parameters:

  • columns (Array) —

    One or more column names.

Returns:



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# File 'lib/polars/functions/lazy.rb', line 97

def count(*columns)
  if columns.empty?
    warn "`Polars.count` is deprecated. Use `Polars.length` instead."
    return Utils.wrap_expr(Plr.len.alias("count"))
  end

  col(*columns).count
end