How to compare two elements in a list in python

09.12.2020

Python Difference Between Two Lists Lists in Python can be performed in different ways, but it depends on the outcome required. Two popular methods of comparison are set and cmp.

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The set function creates an object that is a set object. The cmp function is used to compare two elements or lists and return a value based on the arguments passed. In this tutorial you will learn how to compare two lists with the help of setcmpand difference functions. The set function in Python uses to take an argument and convert it into a set object. It can take arguments like lists, tuples and dictionaries.

The argument is called iterable. The output of elements might not be in the same order because items passed as list were not in order.

At first, we convert a list into the set by using a set function, now we need to check if both the lists are equal or not by using if operator. In the following example, we first convert a list into the set by using set function then we need to differentiate between these two sets by using difference function and use the if condition to check the return value.

In this example, we need to check the elements one by one whether it's available in List 1 or List2. The cmp function is a built-in method in Python used to compare the elements of two lists. The function is also used to compare two elements and return a value based on the arguments passed. This value can be 1, 0 or Note: cmp build to function for python version 2, In python version 3 it is not available. Register Login.

What is set Function in Python? Recommended Posts:.This code runs absolutely fine. And there is nothing wrong with this logic as you write it in many other programming languages. But, this is not the way you write this code in Python. The list is one of the very prominent data structure in Python.

And there are really interesting pieces of stuff you can code with simple two or three lines of code. For me, this is one of the finest reason to be in love with Python. Set is a collection type in Python, just like list and tuple Ref: the difference between list and tuple.

All the elements in the set are unique. So, the task is to find all the unique elements from the list. Otherwise, not. To check if all elements in list are same, you can compare the number of occurrences of any elements in the list with the length of the list. Otherwise, false. If all function returns true means all the elements in the list are equal. Otherwise, not equal. This is all about this post.

I am sure, you find some valuable solutions to your problem. If you think, we can check if all elements in list are same, even by the better way, write in a comment below. I would love that.

In the if statement using set, why enclose the len function in parens? Thanks for tips! It works without parenthesis as well. Enclosing condition with parenthesis inside if statement is not mandatory. It is all about how we do find it comfortable. Python 3. Code snippets in this article are to brainstorm the different ways of doing the same thing and exploring different Python tactics.

Apart from the set solution, none of the proposed solution are stable with respect to null lists.By using our site, you acknowledge that you have read and understand our Cookie PolicyPrivacy Policyand our Terms of Service. The dark mode beta is finally here.

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Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information. In languages I am more familiar with, I would do something like. This ensures we only compare each pair once. For some context, I am doing collision detection on a bunch of objects contained in the list. For each collision detected, a small 'collision' object describing the collision is appended to a list, which another routine then loops through resolving each collision depending on the nature of the two colliding objects.

Obviously, I only want to report each collision once. Now, what is the pythonic way of doing this, since Python favors using iterators rather than looping over indices?

But this clearly picks up each collision twice, which lead to some strange behavior when trying to resolve them. So what is the pythonic solution here? Of course this will generate each pair twice as each for loop will go through every item of the list. You could use some itertools magic here to generate all possible combinations:. You could still write this using index-based item access, equivalent to what you are used to, using nested for loops:.

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Of course this may not look as nice and pythonic but sometimes this is still the easiest and most comprehensible solution, so you should not shy away from solving problems like that.

I think using enumerate on the outer loop and using the index to slice the list on the inner loop is pretty Pythonic:. Your solution is correct, but your outer loop is still longer than needed.

You don't need to compare the last element with anything else because it's been already compared with all the others in the previous iterations. Your inner loop still prevents that, but since we're talking about collision detection you can save the unnecessary check. Using the same language you used to illustrate your algorithm, you'd come with something like this:. Learn more.By using our site, you acknowledge that you have read and understand our Cookie PolicyPrivacy Policyand our Terms of Service.

The dark mode beta is finally here. Change your preferences any time. Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information. It compares all elements in a list to all elements to another list and returns a boolean array. It would do the following:.

Python | Check if two lists have at-least one element common

The closest thing I have found is pd. Hopefully somebody knows. As mentioned in comments thanks Paul Rooney! This is because the lookup operation item in b takes consistent time if b is a set, while every single item has to be compared until a matching one is found if b is a list.

The speed improvement is not very noticeable if b is small, but for a list b containing hundreds of elements, this can be a freat improvement. Because python isn't a primarily numerical or scientific language it doesn't come with some things that are available by default in matlab or R. For example, numpy has an in1d function:. Using list comprehension we can check if the item is in the list of comparison and return True if so else False.

how to compare two elements in a list in python

Learn more. How to compare each element of two lists in python Ask Question. Asked 1 year, 6 months ago. Active 1 year, 6 months ago. Viewed 6k times. Tezcatlipoca Tezcatlipoca 41 1 1 silver badge 3 3 bronze badges. Active Oldest Votes.

Add some explanation.

Compare Two Lists to Highlight Matched Records

Bazingaa Sure. You could make the time complexity linear by making b a set. Bi Rico Bi Rico Related since OP mentioned Pandas and is from Rpd. Series ['word1', 'word2', 'word3', 'word4']. Didn't think this was worth a new answer but would be a good addition to yours.By using our site, you acknowledge that you have read and understand our Cookie PolicyPrivacy Policyand our Terms of Service. The dark mode beta is finally here.

Change your preferences any time. Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information. Use set. Obviously, any artificial performance test should be taken with a grain of salt, but since the set. The easiest way to do that is to use sets :. The following solution works for any order of list items and also supports both lists to be different length. Learn more. How can I compare two lists in python and return matches Ask Question.

Asked 10 years, 7 months ago. Active 1 year, 7 months ago.

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Viewed k times. I want to take two lists and find the values that appear in both. SilentGhost k 52 52 gold badges silver badges bronze badges.

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The answers below all seem wrong to me. What happens if a number is repeated in either list, surely you'd want to know that? Mar 25 '19 at Possible duplicate of How to find list intersection? Active Oldest Votes.

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SilentGhost SilentGhost k 52 52 gold badges silver badges bronze badges. A note of caution, the list comprehension is not necessarily the faster option. Another note of caution: the list comprehension finds the values that appear in both at the SAME positions this is what SilentGhost meant by "order is significant". These are answers to 2 quite different questions How do you do this if your lists are lists of lists i.Using traversal in two lists, we can check if there exists one common element at least in them.

While traversing two lists if we find one element to be common in them, then we return true. After complete traversal and checking, if no elements are same, then we return false.

Python to Find Difference Between Two Lists

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Please Improve this article if you find anything incorrect by clicking on the "Improve Article" button below. Writing code in comment? Please use ide. Given two lists a, b. Check if two lists have at least one element common in them. Python program to check. Recommended Posts: Python Check if two lists have any element in common Python Check if element exists in list of lists Python Check if k occurs atleast n times in a list Python program to check if given value occurs atleast k times Python Count of common elements in the lists Python Print all the common elements of two lists Python Find common elements in list of lists Python program to find common elements in three lists using sets Python Find most common element in a 2D list Python Find most common element in each column in a 2D list Python - Diagonal element addition among lists Python Remove given element from list of lists Python Merge two list of lists according to first element Python Concatenate two lists element-wise Python Merge List with common elements in a List of Lists.

Check out this Author's contributed articles. Load Comments.By using our site, you acknowledge that you have read and understand our Cookie PolicyPrivacy Policyand our Terms of Service. The dark mode beta is finally here. Change your preferences any time. Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information.

I am searching for a way to compare two adjacent items in a list, eg. Any help appreciated, Thank you. EDIT: I am aware of the built in sort function, but just wanted to practice coding and algorithm-writing by creating my own :. You can use zip :. However, do not implement list sorting by yourself!

how to compare two elements in a list in python

There is a really good guide on how to sort things on the python website. If that's not your intention. When you run this with say [1,1,1,1,1,1], it prints 1, when one of numbers doesn't match, it returns False.

Learn more. How to compare two adjacent items in the same list - Python Ask Question. Asked 7 years, 3 months ago. Active 3 years, 6 months ago. Viewed 24k times. Any help appreciated, Thank you EDIT: I am aware of the built in sort function, but just wanted to practice coding and algorithm-writing by creating my own :.

how to compare two elements in a list in python

Do you want to sort your list? Active Oldest Votes. Ashwini Chaudhary Ashwini Chaudhary k 43 43 gold badges silver badges bronze badges. Lattyware actually it's you who beat me by 3 seconds. The quick-and-ugly solution would be this don't use it! ThiefMaster ThiefMaster k 70 70 gold badges silver badges bronze badges. Also, would you mind explaining how that second method you suggested works?

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