How to split list python

Python: Split a List into n Chunks (4 Ways)

Lists in Python are mutable and heterogenous, meaning they can be changed and can contain items of different data types. They are also ordered, meaning their order matters and items can be accessed by their index position.

Knowing how to work with lists in Python is an import skill to learn. Here, you’ll learn how to use Python to split a list into chunks.

The Quick Answer: Use List Indexing

Use a for loop to split a Python list into chunks

Table of Contents

How to Access a Python List by Its Index

One of the many wonderful properties of lists, is that they are ordered. This means that we can access an item, or a range of items, by its index. Let’s see how Python list indices work:

Split Lists into Chunks Using a For-Loop

For-loops in Python are an incredibly useful tool to use. They make a lot of Python methods easy to implement, as well as easy to understand.

For this reason, let’s start off by using a for-loop to split our list into different chunks.

One of the ways you can split a list is into n different chunks. Let’s see how we can accomplish this by using a for loop:

Let’s take a look at what we’ve done here:

We can see that this is a fairly straightforward way of breaking a Python list into chunks. Next, you’ll learn how to do accomplish this using Python list comprehensions.

Want to learn more? If you’d like to learn more about Python for-loops, check out my in-depth tutorial here, which will teach you all you need to know!

Split Python Lists into Chunks Using a List Comprehension

In many cases, Python for-loops can be rewritten in a more Pythonic way by writing them as one-liners called list comprehensions. List comprehensions in Python have a number of useful benefits over for-loops, including not having to instantiate an empty list first, and not having to break your for-loop over multiple lines.

To learn more about list comprehensions in Python, check out my YouTube tutorial below:

Let’s see how we can write a Python list comprehension to break a list into chunks:

Before we break down this code, let’s see what the basic syntax of a Python list comprehension looks like:

How List Comprehensions work in Python

Now let’s break down our code to see how it works:

While this approach is a little faster to type, whether or not it is more readable than a for-loop, is up for discussion. Let’s learn how to split our Python lists into chunks using numpy.

Want to learn more? Check out my in-depth tutorial about Python list comprehensions by clicking here!

Split Lists into Chunks Using numpy

In this section of the tutorial, we’ll use the numpy array_split() method to split our Python list into chunks.

Let’s see how we can use numpy to split our list:

This is a fairly long way of doing things, and we can definitely cut it down a little bit. Let’s see how that can be done:

Let’s break this down a little bit:

Want to learn more about division in Python? Check out my tutorial on how to use floored integer division and float division in Python in this tutorial here.

Split Lists into Chunks Using Itertools

Let’s see how we can use itertools library to split a list into chunks. In particular, we can use the zip_longest function to accomplish this.

Let’s see how we can do this:

We can see here that we can have a relatively simple implementation that returns a list of tuples. Notice one of the things that’s done here is split the list into chunks of size n, rather than into n chunks.

Conclusion

How to Split List in Python

A list can be split based on the size of the chunk defined. Splitting a list into n parts returns a list of n lists containing an equal number of list elements. If the number of lists, n, does not evenly divide into the length of the list being split, then some lists will have one more element than others.

Let’s traditionally split the list.

Python list split

To split a list in Python, call the len(iterable) method with iterable as a list to find its length and then floor divide the length by 2 using the // operator to find the middle_index of the list.

Output

As you can see from the output, we split the list in the exact half. We used the colon operator(:) to access the first and second half of the split list.

How to split a list into n parts in Python

To split a list into n parts in Python, use the numpy.array_split() function. The np.split() function splits the array into multiple sub-arrays.

The numpy array_split() method returns the list of n Numpy arrays, each containing approximately the same number of elements from the list.

Output

In this example, we split the list into 3 parts.

Split a List Into Even Chunks of N Elements in Python

A list can be split based on the size of the chunk defined. This means that we can determine the size of the chunk. If the subset of a list doesn’t fit in the size of the defined chunk, fillers need to be inserted in the place of the empty element holders. We will be using None as filters to fill in those empty element holders.

Output

The list has been split into equal chunks of 7 elements each.

The above list_split() function takes the arguments: listA for the list and chunk_size for a number to split it by. Then, the function iterates through the list with an increment of the chunk size n.

Each chunk is expected to have the size given as an argument. If there aren’t enough elements to split the same size, the remaining unused elements are filled with None.

Split list into smaller lists (split in half)

I am looking for a way to easily split a python list in half.

So that if I have an array:

I would be able to get:

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If you want a function:

A little more generic solution (you can specify the number of parts you want, not just split ‘in half’):

If you don’t care about the order.

list[::2] gets every second element in the list starting from the 0th element.
list[1::2] gets every second element in the list starting from the 1st element.

Using list slicing. The syntax is basically my_list[start_index:end_index]

..and the swap the values around to get the second half:

Here is a common solution, split arr into count part

I tested, and the double slash is required to force int division in python 3. My original post was correct, although wysiwyg broke in Opera, for some reason.

If you have a big list, It’s better to use itertools and write a function to yield each part as needed:

You can use this like:

This code snippet is from the python itertools doc page.

This is similar to other solutions, but a little faster.

General solution split list into n parts with parameter verification:

With hints from @ChristopheD

10,000 rows and it finishes in a fraction of second.

Just my two cents.

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Python Split list into chunks

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In this tutorial, you will learn how to split a list into chunks in Python using different ways with examples.

Python Split list into chunks

Lists are mutable and heterogenous, meaning they can be changed and contain different data types. We can access the elements of the list using their index position.

There are five various ways to split a list into chunks.

Method 1: Using a For-Loop

The naive way to split a list is using the for loop with help of range() function.

Output

Method 2: Using the List Comprehension Method

The list comprehension is an effective way to split a list into chunks when compared to for loop, and it’s more readable.

We have a sample_list and contain ten elements in it. We will split the list into equal parts with a chunk_size of 2.

Output

Method 3: Using the itertools Method

We can leverage the itertools module to split a list into chunks. The zip_longest() function returns a generator that must be iterated using for loop. It’s a straightforward implementation and returns a list of tuples, as shown below.

Output

Method 4: Using the NumPy Method

We can use the NumPy library to divide the list into n-sized chunks. The array_split() function splits the list into sublists of specific size defined as n.

Output

Method 5: Using the lambda Method

We can use the lambda function to divide the list into chunks. The lambda function will iterate over the elements in the list and divide them into N-Sized chunks, as shown below.

Split List Into Chunks in Python

One of the Python data structures that can contain mixed values or elements within it is called lists. This article will introduce various ways to split a list into chunks. You can use any code example that fits your specifications.

Split List in Python to Chunks Using the List Comprehension Method

We can use list comprehension to split a Python list into chunks. It is an efficient way to encapsulate the operations to make the code easier to understand.

The complete example code is given below.

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Split List in Python to Chunks Using the itertools Method

This method provides a generator that must be iterated using a for loop. A generator is an efficient way of describing an iterator.

[iter(iterable)]*n generates one iterator and iterated n times in the list. A round-robin of every iterator is then effectively done by izip-longest ; since this is a similar iterator, each such call is advanced, resulting in each such zip-round-robin producing one tuple of n objects.

Split List in Python to Chunks Using the lambda Function

It is possible to use a basic lambda function to divide the list into a certain size or smaller chunks. This function works on the original list and N-sized variable, iterate over all the list items and divides it into N-sized chunks.

The complete example code is given below:

Split List in Python to Chunks Using the lambda & islice Method

A lambda function can be used with the islice function and produce a generator that iterates over the list. The islice function creates an iterator that extracts selected items from the iterable. If the start is non-zero, the iterable elements will be skipped before the start is reached. Elements are then returned consecutively unless a step is set higher than one that results in the skipping of items.

The complete example code is given below:

Split List in Python to Chunks Using the NumPy Method

The complete example code is given below:

The arange function ordered the values according to the given argument and the array_split() function produces the list/sub-arrays based on the parameter given in it as a parameter.