• Skip to secondary menu
  • Skip to main content
  • Skip to primary sidebar

Python and R Tips

Learn Data Science with Python and R

  • Home
  • Python
  • Pandas
    • Pandas 101
  • tidyverse
    • tidyverse 101
  • R
  • Linux
  • Conferences
  • Python Books
  • About
    • Privacy Policy
You are here: Home / Python / Three Ways to Merge (or flatten) Lists in Python

Three Ways to Merge (or flatten) Lists in Python

April 30, 2017 by cmdlinetips

Often you may have to flatten a list of lists or merge multiple lists into a single list in python. Obviously there are multiple ways to go about it. Here are three ways to flatten or merge lists in to a list.

Merge with “+” Operator”

If you have three separate lists like [1, 2, 3], [4, 5, 6], [7, 8, 9], you can merge in to a single list using + operator like

> [1, 2, 3] + [4, 5, 6] + [7, 8, 9]
> [1, 2, 3, 4, 5, 6, 7, 8, 9]

Note that the use of “+” to merge lists preserves any duplicates present in multiple lists. For example, the duplicate “4” will be in the merged list.

> [1, 2, 3, 4] + [4, 5, 6] + [7, 8, 9]
> [1, 2, 3, 4, 4, 5, 6, 7, 8, 9]

Flatten with “sum” Operator”

If you have a list of lists, we can use the sum operator to merge lists

> lol= [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
> sum(lol , [])
> [1, 2, 3, 4, 5, 6, 7, 8, 9]

Merging/Collapsing/Flattening a list of lists with list comprehensions

We can use list comprehensions in python to merge/collapse/flatten a list of lists.

> lol= [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
> [i for l in lol for i in l]
> [1, 2, 3, 4, 5, 6, 7, 8, 9]

Share this:

  • Click to share on Facebook (Opens in new window) Facebook
  • Click to share on X (Opens in new window) X

Related posts:

Default ThumbnailMastering Lists in Python Using List Comprehensions Default Thumbnail3 Ways to Write Text to a File in Python Default Thumbnail3 Ways to Read A Text File Line by Line in Python Default ThumbnailHow To Merge/Join DataFrames with Pandas in Python?

Filed Under: Python, Python List Comprehensions, Python Tips Tagged With: Merge a list of lists in Python, Python

Primary Sidebar

Subscribe to Python and R Tips and Learn Data Science

Learn Pandas in Python and Tidyverse in R

Tags

Altair Basic NumPy Book Review Data Science Data Science Books Data Science Resources Data Science Roundup Data Visualization Dimensionality Reduction Dropbox Dropbox Free Space Dropbox Tips Emacs Emacs Tips ggplot2 Linux Commands Linux Tips Mac Os X Tips Maximum Likelihood Estimation in R MLE in R NumPy Pandas Pandas 101 Pandas Dataframe Pandas Data Frame pandas groupby() Pandas select columns Pandas select_dtypes Python Python 3 Python Boxplot Python Tips R rstats R Tips Seaborn Seaborn Boxplot Seaborn Catplot Shell Scripting Sparse Matrix in Python tidy evaluation tidyverse tidyverse 101 Vim Vim Tips

RSS RSS

  • How to convert row names to a column in Pandas
  • How to resize an image with PyTorch
  • Fashion-MNIST data from PyTorch
  • Pandas case_when() with multiple examples
  • An Introduction to Statistical Learning: with Applications in Python Is Here
  • 10 Tips to customize ggplot2 title text
  • 8 Plot types with Matplotlib in Python
  • PCA on S&P 500 Stock Return Data
  • Linear Regression with Matrix Decomposition Methods
  • Numpy’s random choice() function

Copyright © 2025 · Lifestyle Pro on Genesis Framework · WordPress · Log in

Go to mobile version