Polars Series len() Function with Examples

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  • Post last modified:July 2, 2025
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In Polars, the len() function returns the number of elements contained in a Series. A Polars Series is a single column of data, a named list of values, much like a column in a Pandas DataFrame.

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In this article, I will explain the syntax of the Polars Series len() function, its parameters, and how it returns the number of elements in the Series as an integer.

Key Points –

  • The len() function returns the number of elements (rows) contained in a Polars Series.
  • It is equivalent to the len() method and can be used interchangeably.
  • The return value is always an integer (int) representing the count of elements.
  • len() counts all elements, including null (missing) values.
  • You can use Python’s built-in len(series) syntax or the Polars method series.len().
  • Series.len() is functionally equivalent to len(series) and series.shape[0].

Polars Series len() Introduction

Let’s know the syntax of the series len() function.


# Syntax of len()
Series.len() → int

Parameters of the Polars Series len()

No arguments are needed, just empty parentheses ().

Return Value

This function returns an integer (int) representing the number of elements in the Series.

Usage of Polars Series len() Function

The len() function retrieves the total number of elements (or rows) present in a Polars Series. It returns this count as an integer value.

Now, let’s create a Polars series using a list of values and use the len() function.


import polars as pl

ser = pl.Series("numbers", [2, 4, 6, 8])
print("Original Series:\n", ser)

Yields below output.

polars series len

The basic usage of the Polars Series len() function involves calling it in the simplest way to retrieve the count of elements in a Series.


# Get the length
ser2 = ser.len()
print("Length of Series:", ser2)

Here,

  • ser.len() returns the number of elements (4).
  • This is the simplest way to check how many values your Series contains.
polars series len

Series with Null Values

The Series.len() function counts every element in the Series, including any null values. It returns the total number of rows, not just those with valid (non-null) data. In Polars, a null represents missing or undefined information. In Python, this is written as None, and it appears as null within Polars.


import polars as pl

# Series with null values
ser = pl.Series("values", [2, None, 4, None, 6])

# Series with null values
ser2  =  ser.len()
print("Length of Series:", ser2)

# Output:
# Length of Series: 5

Here,

  • There are 5 elements in the Series.
  • 2 of them are null, but len() still returns 5.

Series with Strings

A Series containing strings is essentially a column-like data structure that holds text values. Below is an example of a Polars Series with string entries and how to determine its length.


import polars as pl

# Create a Series of strings
ser = pl.Series("fruits", ["apple", "banana", "mango", "grape"])

# Get the length
print("Length of series:", ser.len())

# Output:
# Length of series: 4

Here,

  • The len() function still counts all elements, regardless of whether the values are strings, numbers, or nulls.

Empty Series in Polars

An empty Series is one that contains no elements at all. Below is an example of an empty Polars Series and how the len() function responds to it.


import polars as pl

# Create an empty Series
ser = pl.Series("empty", [])
print("Length of series:", ser.len())

# output:
# Length of series: 0

Here,

  • When a Series has no elements, len() returns 0.
  • This is useful to check for empty data before processing.

Conclusion

In conclusion, the len() function in Polars is a simple yet essential tool for quickly determining the number of elements in a Series, including any null values. Whether your Series contains numbers, strings, or is empty, len() provides an accurate count to help you better understand and work with your data.

Happy Learning!!

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