Method: Polars::Functions#len

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

#len ⇒ Expr Also known as: length

Return the number of rows in the context.

This is similar to COUNT(*) in SQL.

Examples:

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

Generate an index column by using len in conjunction with int_range.

df.select([
  Polars.int_range(Polars.len, dtype: Polars::UInt32).alias("index"),
  Polars.all
])
# =>
# shape: (3, 4)
# ┌───────┬──────┬──────┬─────┐
# │ index ┆ a    ┆ b    ┆ c   │
# │ ---   ┆ ---  ┆ ---  ┆ --- │
# │ u32   ┆ i64  ┆ i64  ┆ str │
# ╞═══════╪══════╪══════╪═════╡
# │ 0     ┆ 1    ┆ 3    ┆ foo │
# │ 1     ┆ 2    ┆ null ┆ bar │
# │ 2     ┆ null ┆ null ┆ foo │
# └───────┴──────┴──────┴─────┘

Returns:



44
45
46
 
# File 'lib/polars/functions/len.rb', line 44

def len
  Utils.wrap_expr(Plr.len)
end