Count unique values in list python
In this tutorial, you’ll learn how to use Python to count unique values in a list. You’ll also learn what the fastest way to do this is! You’ll learn how to accomplish this using a naive, brute-force method, the Show
The Quick Answer: Use Python Sets
Python lists are a useful built-in data structure! One of the perks that they offer is the ability to have duplicate items within them. There may be many times when you may to count unique values contained within a list. For example, if you receive data in a list that tracks the number of log in into a site, you could determine how many unique people actually logged in. Using Collections to Count Unique Values in a ListThe built-in Because of this, we can counts the number of keys to count the number of unique values. Tip! Want to learn more about the Python collections module and its Counter class? Check out my in-depth tutorial here, where you’ll learn how to count occurrences of a substring in a string. Let’s see how we can use the
Let’s see what we’ve done here:
We can make this much easier to write by simply chaining the process together, as shown below.
This process returns the same thing, but is much quicker to write! Using Sets to Count Unique Values in a Python ListAnother built-in data structure from Python are sets. One of the things that separate sets from lists is that they can only contain unique values. Python comes built with a Now, let’s see how we can use sets to count unique values in a list:
What we’ve done here is:
We can also make this process a little faster by simply chaining our methods together, as demonstrated below:
This returns the same value but is a little faster to write out. Want to learn more? Learn four different ways to append to a list in Python using this extensive tutorial here. Use Numpy to Count Unique Values in a Python ListYou can also use numpy to count unique values in a list. Numpy uses a data structure called a numpy array, which behaves similar to a list but also has many other helpful methods associated with it, such as the ability to remove duplicates. Let’s see how we can use numpy to count unique values in a list:
Let’s see what we’ve done here:
We can also write this out in a much faster way, using method chaining. Let’s see how this can be done:
This returns the same result as before. Use a For Loop in Python to Count Unique Values in a ListFinally, let’s take a look at a more naive method to count unique items in a list. For this, we’ll use a Python for loop to iterate over a list and count its unique items.
Let’s see what we’ve done here:
Check out some other Python tutorials on datagy, including our complete guide to styling Pandas and our comprehensive overview of Pivot Tables in Pandas! What Method is Fastest to Count Unique Values in a Python List?Now that you’ve learned four unique ways of counting unique values in a Python list, let’s take a look at which method is fastest. What we’ll do is create a Python decorator to time each method. We’ll create a function that executes each method and decorate it to identify how long its execution takes. For out sample list, we’ll use the first few paragraphs of A Christmas Carol, where each word is a list, and multiply that list by 10,000 to make it a bit of a challenge:
From this, we can see that while the Counter method and the Numpy methods are reasonably fast, the set method is the fastest of the bunch! This could be attributed to the fact that it doesn’t require the import of another method. ConclusionIn this post, you learned how to count unique values in a Python list. You learned how to do this using built-in sets, using the To learn more about the Counter object in the collections module, you can check out the official documentation here. How do you count unique values in a list?You can use the combination of the SUM and COUNTIF functions to count unique values in Excel. The syntax for this combined formula is = SUM(IF(1/COUNTIF(data, data)=1,1,0)). Here the COUNTIF formula counts the number of times each value in the range appears. The resulting array looks like {1;2;1;1;1;1}.
How do I count unique values in a column in pandas?How to count unique items in pandas. pandas provides the useful function value_counts() to count unique items – it returns a Series with the counts of unique values. ... . From the output of line 10 you can see the result, which is a count of the column col1 .. Category data value count with normalize.. What does unique () do in Python?unique() function. The unique() function is used to find the unique elements of an array. Returns the sorted unique elements of an array.
How do you find the number of elements in a list in Python?The most straightforward way to get the number of elements in a list is to use the Python built-in function len() . As the name function suggests, len() returns the length of the list, regardless of the types of elements in it.
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