![]() 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. If it isn’t, then we append it to the list and add 1 to our counter unique_itemsĬheck 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?.We then loop over our original list and see if the current item is in the unique_list.We create a new list called unique_list and an integer of 0 called unique_items.For this, we’ll use a Python for loop to iterate over a list and count its unique items. Use a For Loop in Python to Count Unique Values in a Listįinally, let’s take a look at a more naive method to count unique items in a list. Num_values = len(np.unique(np.array(a_list))) Let’s see how this can be done: # Use numpy in Python to count unique values in a list We can also write this out in a much faster way, using method chaining. Finally, we calculated the length of that array.We used the unique() function from numpy to remove any duplicates.We imported numpy as np and created an array using the array() function.Let’s see how we can use numpy to count unique values in a list: # Use numpy in Python 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. You can also use numpy to count unique values in a list. Use Numpy to Count Unique Values in a Python List Want to learn more? Learn four different ways to append to a list in Python using this extensive tutorial here. This returns the same value but is a little faster to write out. We can also make this process a little faster by simply chaining our methods together, as demonstrated below: # Using sets to count unique values in a list Returned the number of values by counting the length of the set, using the len() function.Turned our list into a set using the built-in set() function. ![]() Now, let’s see how we can use sets to count unique values in a list: # Using sets to count unique values in a list When we pass a list into the function, it turns the list into a set, thereby stripping out duplicate values. Python comes built with a set() function that lets you create a set based on something being passed into the function as a parameter. One of the things that separate sets from lists is that they can only contain unique values. This process returns the same thing, but is much quicker to write! Using Sets to Count Unique Values in a Python ListĪnother built-in data structure from Python are sets. # Using Counter from collections to count unique values in a list ![]() We can make this much easier to write by simply chaining the process together, as shown below.
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