Python find second occurrence in list. a = [1. Examples: Tuple: (10, 8, 5, 2, 10, 15,...
Python find second occurrence in list. a = [1. Examples: Tuple: (10, 8, 5, 2, 10, 15, 10, 8, 5, 8, 8, 2) Input : 4 Output : 0 times Input : 10 Output : 3 times In Python 3, filter doesn't return a list, but a generator-like object. But this method is very efficient when finding all occurrences of elements. The rfind() method is almost the same as the rindex() method. Using list Jul 30, 2021 · Finding the First Occurence of the Element Let’s begin by looking for the first occurrence of the element in a Python array. Python also provides many functions or methods for working with lists. Includes practical examples! Jan 24, 2025 · Learn how to find the second occurrence of a substring in a Python string using find(), index(), and regular expressions methods. If the search string does not occur twice, -1 should be returned. We aim to find the very first position at which the element occurs in a list of elements (array). Feb 28, 2022 · Python List Index: Find First, Last or All Occurrences February 28, 2022 In this tutorial, you’ll learn how to use the Python list index method to find the index (or indices) of an item in a list. Fortunately, Python provides multiple approaches to solve this problem efficiently. using cumsum and where, but I'd like to know if there's a numpy-free way to solve the problem. vultr. Let’s explore the efficient methods to find duplicates. For each queries [i], you need to find the index of the queries [i]th occurrence of x in the nums array. Output: Gfg is best. 5, 7, 1. Dec 1, 2011 · Note that x. Input : test_str = 'geekforgeeks', K = "e", N = 2 Output : kforgeeks Explanation : After 2nd occur. Jul 18, 2018 · Are you unaware of list indexing? sublist[0]? You're using a really weird way to get the first item of a list. Jun 12, 2013 · Is there a Python-way to split a string after the nth occurrence of a given delimiter? Given a string: '20_231_myString_234' It should be split into (with the delimiter being '_', after its second index() will give the first occurrence of an item in a list. docs. The function returns the index of the nth occurrence or -1 if it is not found. Python String count () Method Count of elements matching particular condition in Python Count Occurrences of Specific Value in Pandas Apr 9, 2025 · In Python programming, being able to find the index of an element's occurrence within a sequence (such as a list, string, or tuple) is a common task. We pass the programming_languages list to the enumerate method which goes over each item in list and returns a tuple containing the index and item of the list at that index. Jun 2, 2024 · While Python provides a built-in split() function to achieve this, it splits the string at every occurrence of the delimiter. , 7. Aug 23, 2021 · Find the index of an element in a list using the index () method We can use the index () method to find the first occurrence of an element in a list. You have created a second variable that points to the exact same physical memory block. Aug 16, 2024 · In this article, we will discuss different methods (find, split, and regular expression module) for finding the second occurrence of a substring in a Python string. 6, 9999. If there are fewer than queries [i] occurrences of x, the answer should be -1 for that query. Python provides built-in methods that allow you to locate the first occurrence of a substring. The NumPy library contains multidimensional array data structures, such as the homogeneous, N-dimensional ndarray, and a large library of functions that operate efficiently on these data Jan 18, 2014 · You can use the count method of the strings to find the number of occurrences of the user_input in the string. find("substring", 2nd) How can you achieve this in Python? index() will give the first occurrence of an item in a list. See example below. The indices are stored in the list of indices. Using rindex () to find last occurrence of substring rindex () method returns the last occurrence of the substring if present in the string. You might want to go through the Python tutorial, or browse the docs for the built-in types and functions a bit. find(substring) + 1) Jul 12, 2025 · For example, we are given a list a = [10, 20, 30, 20, 40, 30, 50] we need to find indices of the duplicate items so that output should be {20: [1, 3], 30: [2, 5]}. Gfg also has Classes now. Does anyone know how I can get the index position of duplicate items in a python list? I have tried doing this and it keeps giving me only the index of the 1st occurrence of the of the item in the list. You can call the function using the test cases in the table below. Feb 2, 2024 · We'll discuss several ways to find the nth occurrence of a substring in a string. I’ll also show you a funct A common challenge arises when we want to determine the second-largest number from a list. index returns the first occurrence or the first occurrence after some point, and therefore as far as I can tell is not a solution. Mar 15, 2022 · I’ve been trying to figure out how to find the index number of the second occurrence of a list of numbers and then print from 0 index to the second occurrence number’s index from that list. Using List Comprehension List comprehension is an Feb 13, 2020 · Does this answer your question? How to find and replace nth occurrence of word in a sentence using python regular expression? This is a great answer, exactly what I needed and bonus points for the timings! I was trying to quickly find the outlier class in an output from tensorflow. Learn how to find the second occurrence of a specific substring in a string using Python. functions were used. Nov 13, 2023 · Method 1: Using the reversed () function One straightforward way to find the last occurrence of an item in a Python list is by using the reversed () function in combination with the index () method. count(0))-1 You can increase the number to -2 or -3 to find the position of the desired number from last eg: a. Then, use the str. The index () method takes the element as the first input argument which is compulsory. g. Is there a neat trick which returns all indices in a list for an element? Oct 28, 2025 · This method is not efficient for finding occurrence of single element because it requires O (n) extra space to create a new dictionary. Whether you are parsing data, searching through text, or working with collections of values, knowing how to locate the position of a particular item can be crucial. Regular expression tester with syntax highlighting, explanation, cheat sheet for PHP/PCRE, Python, GO, JavaScript, Java, C#/. Input : test_str = 'geekforgeeks', K = "e", N = 4 Output : ks Explanation : After 4th occur. The method replicates the behavior of the indexOf () method in many other languages, such as JavaScript. secondIndexOf('White Rabbit', 'it') should return 10 . Jul 11, 2025 · This approach uses a regular expression to search for the first occurrence of the substring in the input string, and returns the portion of the string after the substring if it is found. I'm new to python and any help will be appreciated. This method is quick and easy for single occurrences and small lists, but it lacks the efficiency of some of the other methods for repeated searches or very large lists. , 5. Regex match second occurrence: Learn how to use regex to match the second occurrence of a pattern in a string. Feb 6, 2009 · Is there any built-in methods that are part of lists that would give me the first and last index of some value, like: Apr 10, 2024 · If you need to find the indices of the duplicate items in a list with a start index: Use a while True loop to iterate until the occurrences of the item are found. Apr 6, 2023 · Python has several methods and hacks for getting the index of an item in iterable data like a list, tuple, and dictionary. May 13, 2024 · The article shows methods on how to find first occurrence of a value in a column in excel. ) occurrence of term in s. Aug 31, 2012 · I updated my question. Use the list. If v is not found for at least two times, return the N Jan 24, 2025 · Learn how to find the second occurrence of a substring in a Python string using find(), index(), and regular expressions methods. Method #1 : Using split () This is one of the ways in which this task can Jul 23, 2025 · Method 2 (Use Hashing): In this method, we store all elements of second array in a hash table (unordered_set). In other words, if there are more than 1 duplicated numbers, return the number for which the second occurrence has a smaller index than the second occurrence of any other number does. I’ll also show you a funct Oct 30, 2019 · Hi coders, continue with my study on JS and I found this exercise: Write a function secondIndexOf , taking two strings and determining the second occurrence of the second string in the first string. One by one check all elements of first array and print all those elements which are not present in the hash table. Using Loop Use a loop (for loop) to iterate over the list and keep two variables max1 and max2 to keep track of largest and second largest number of Jan 18, 2014 · You can use the count method of the strings to find the number of occurrences of the user_input in the string. Apr 8, 2022 · 1 I need to find the second occurrence of a substring. Mar 8, 2014 · As you can see, it will raise an StopIteration exception in case it can't find a match. For example, consider a string s = "Geeks" and character k = 'e', in the string s, the first occurrence of the character 'e' is at index1. I need help to see why doesn't my program work correctly. Nov 13, 2023 · Learn how to find the index of an item in a list using the index function, enumerate function, and Numpy module in python. Jan 29, 2023 · How to find the location of the nth occurrence of an element in a python list Asked 2 years, 10 months ago Modified 2 years, 10 months ago Viewed 160 times Definition and Usage The rfind() method finds the last occurrence of the specified value. While working with the strings, the common requirement is searching for a specific substring within a larger string. Jul 15, 2017 · Given an array a that contains only numbers in the range from 1 to a. Using a Set (Most Efficient for Large Lists) Set () method is used to set a track seen elements and helps to identify duplicates. Unlike arrays in some languages, Python lists are very flexible: Can contain duplicate items Mutable: items can be modified, replaced, or removed Ordered: maintains the order in which items are added Index-based: items are accessed using their position (starting from 0) Can store mixed data types Watch short videos about how to find second largest number in list python from people around the world. Find Occurrences of an Element in an Array - You are given an integer array nums, an integer array queries, and an integer x. Classes help understand better. The built-in index() method can find the first occurrence of a value. Using a loop and a dictionary We iterate through the list using enumerate() and store indices of each element in a dictionary appending new indices if element appears again. var secondIndexOf = function(s1, s2 ){ var firstIndex = s1. Example: Input: Gfg is best. Mar 8, 2014 · 0 You can use this to find in last position where a is the array t=(a. This can be done in various ways, but in this article, we will see how this can be done using a simple approach and how inbuilt functions can be used to solve this problem. The index() method searches an element in the list and returns its position Apr 26, 2023 · Given a String, extract the string after Nth occurrence of a character. Jan 10, 2026 · In Python, a list is a built-in data structure that can hold an ordered collection of items. find(substring, string. (in the case above it would be 7. indexOf(s2 Sep 15, 2021 · Learn how to find the first occurrence of one list within another list in Python with examples and detailed explanation. predict_cluster_index (input_fn)) is an array with no help functions to access the cluster with the highest occurrences. , 3. I mean something like we give the input to the function as 2 (2nd occurrence, or maybe 1 in Python's interpretation since it starts from 0) and the output is 9 If we give the input as 1, the output should be 4, 192 This seems like it should be pretty trivial, but I am new at Python and want to do it the most Pythonic way. Nov 7, 2025 · In this article, we will discuss how to replace only the duplicate occurrences of certain words in a string that is, replace a word from its second occurrence onwards, while keeping its first occurrence unchanged. Please write a program which finds the second occurrence of a substring. val==5. In this tutorial, you will learn about the Python index() function. index (sub,start) method for each occurrence of the user_input in the word and increment start by 1 each time so that you do not wind up getting the same index each time. NET, Rust. This blog post will explore different ways to find the index of occurrence in Feb 28, 2022 · Python List Index: Find First, Last or All Occurrences February 28, 2022 In this tutorial, you’ll learn how to use the Python list index method to find the index (or indices) of an item in a list. Below is my code. nlargest function is mentioned but since I . There is also a solution in numpy for cases similar to the above, e. Feb 17, 2013 · 1 I have a list of strings (about 100), and I want to find the first occurence of one of them in another string and the index in which it occurred. of "e" string is extracted. If you find a second occurrence of v, return that non-negative index. The occurrences cannot overlap. Oct 9, 2016 · Given a list of Python values xs and a value v, search through xs for v. sort() for more inbuilt function in list click here 192 This seems like it should be pretty trivial, but I am new at Python and want to do it the most Pythonic way. You can also use We would like to show you a description here but the site won’t allow us. 3, 2. We have used two python functions, find() and split() and a regular expression method to find to nth occurrence of a substring. If you write backup_list = primary_list, you have not duplicated the list. Like in C++ we can use lower and upper bound to find the last occurrence of the number. One common and versatile structure is a list, which can hold different types of data in a specific order. Ins Number, Python, Python List And More Watch short videos about second largest number in list python from people around the world. It also has Classes now. 1, 9999. Python offers various methods to achieve this efficiently. There's got to be something equivalent to what I WANT to do which is mystring. But what if the substring appears multiple times. I'm playing with the method find and slicing strings. I want to find the index corresponding to the n'th occurrence of a substring within a string. May 2, 2022 · Here we use list comprehension and the index method to find the index of "Python" in each of the sublists. In this article, we are looking at how you can get the index of a list item with the index() method. Finding the first occurrence If you only want the first thing that matches a condition (but you don't know what it is yet), it's fine to use a for loop (possibly using the else clause as well, which is not really well-known). Oct 28, 2025 · For example: li = [10, 20, 4, 45, 99] -> Second largest number = 45 li = [5, 8, 12, 3, 7] -> Second largest number = 8 Let's explore other different method to find second largest number in a list. Mar 5, 2024 · Using Python’s built-in index() method in a one-liner, we can search for the first occurrence with a combination of slicing and index searching. find(substring) + 1) Oct 6, 2010 · The following function finds all the occurrences of a string inside another while informing the position where each occurrence is found. contrib. index() method to get the index of each occurrence by specifying a start index. In this exercise the occurrences cannot overlap. I’ve been trying to figure out how to find the index number of the second occurrence of a list of numbers and then print from 0 index to the second occurrence number’s index from that list. Jul 23, 2025 · Using List Comprehension List comprehension allows for a concise and efficient way to find indices. index(0)+a. I recognised that sometimes SectionTitle0 (former 'Tech-C') and SectionTitle1 (former 'Zone-C') are identically. In this article, we’ll explore several methods to find the second-largest number in Python, each with step-by-step explanations and code examples. Jul 13, 2018 · . factorization. Jul 11, 2025 · The variation of getting the last occurrence of the string is discussed here. In Python, there are several ways to do this. Jul 11, 2025 · In Python, it is common to locate the index of a particular value in a list. 4, 9999. length, find the first duplicate number for which the second occurrence has the minimal index. Append the matching indices to a new list. Definition and Usage The rfind() method finds the last occurrence of the specified value. com Jul 23, 2025 · Finding duplicates in a list is a common task in programming. Let's discuss certain ways in which we can find the last occurrence of substring in string in Python. You can also pass a default argument to next() function to return a default value instead of raising exception. I keep the index, and afterwords search again using another word list from that index on, and back to the first list until it reaches the end of the string. Upon each iteration, if the loop variable attains the value same that of received from the user and stored in the variable the_item, the variable how_many_times gets incremented by 1. Is there a neat trick which returns all indices in a list for an element? Jul 13, 2023 · The function iteratively searches for the next occurrence of sub_string using the find() method, updating the starting index until the desired occurrence is found. By iterating through the list enumerate () we can collect the indices where the element matches. Using Loop Use a loop (for loop) to iterate over the list and keep two variables max1 and max2 to keep track of largest and second largest number of Thank you for the answer, but, That would give all the occurrences. 7 ,6. 2, 9999. In this tutorial, you'll learn about the best ways to get the first match from a Python list or iterable. Includes practical examples! We would like to show you a description here but the site won’t allow us. This is a powerful technique for extracting data from text or validating input. Jul 13, 2023 · The function iteratively searches for the next occurrence of sub_string using the find() method, updating the starting index until the desired occurrence is found. Feb 13, 2020 · Does this answer your question? How to find and replace nth occurrence of word in a sentence using python regular expression? Jul 11, 2025 · Given a string and a character, our task is to find the first position of the occurrence of the character in the string using Python. e. Nov 3, 2022 · In this program, we need to accept a tuple and then find the number of times an item is present in the tuple. They help understand better. KMeansClustering (). index searches through the list in order until it finds a match then and stops. It takes two optional arguments which are indices at which search has to start and stop in the list. Discover essential tips and tricks to make your coding easier and more efficient. Jan 15, 2026 · The idea is to use inbuilt functions to find the first and last occurrence of the number in the array arr []. The rfind() method returns -1 if the value is not found. For example, in the string "aaaa" the second occurrence of the substring "aa" is at index 2. But what if we only want to split the string after the second occurrence? In this article, we will explore different approaches to accomplish this task in Python 3 without the need for any external libraries or extensions. Explore efficient Python techniques for finding the first occurrence of elements in lists, including indexing, searching strategies, and practical code examples for developers. find("substring", 2nd) How can you achieve this in Python? Apr 8, 2010 · In order to check its Occurrence, I ran a for loop in the list named x. If there is no second (or first) occurrence, the program should print out a message accordingly. However, there are scenarios where multiple occurrences of the value exist and we need to retrieve all the indices. 4) in the most efficient way possible (my list can get quite big) In this question Retrieve the two highest item from a list containing 100,000 integers the heapq. May 26, 2023 · I am doing some python lately and came up with this exercise if someone could help: Delete every second occurrence (i. , 2nd, 4th, 6th, etc. Python, Python List, Largest Number And More Python lists store multiple data together in a single variable. For example, consider the string "Welcome to the Tutorialspoint to". The index() method searches an element in the list and returns its position Sep 15, 2021 · Learn how to find the first occurrence of one list within another list in Python with examples and detailed explanation. That makes it a little bit more complicated. I've been searching for printing characters before the occurrence of the first string and after the occurrence of the second instance of the string ('-') with no luck (constructing an if statement as you suggested). Mar 28, 2025 · In Python, a data structure helps you organize and store data efficiently. Jun 5, 2021 · # find index of second occurence of substring in string idx = string. In this tutorial, we will learn about Python lists (creating lists, changing list items, removing items, and other list operations) with the help of examples. One of the most devastating logical traps in the Python ecosystem stems from the fact that variables pointing to lists are merely referencing memory addresses. COUNTIF, IF, FREQUENCY etc. Mar 5, 2024 · Problem Formulation: In Python, it is a common problem to find the distance between the nearest occurrences of two elements within a list. Then you'll finish up by creating a reusable function for all your first matching needs. The reversed () function returns an iterator that yields items in reverse order, allowing us to iterate over the list from the end. What would be the most elegant and efficient way of finding/returning the first list item that matches a certain criterion? For example, if I have a list of objects and I would like to get the first object of those with attribute obj. The output for the list (kmeans. If you expect to need indices of more matches, you should use a list comprehension. Is there a way to specify a regular expression to match every 2nd occurrence of a pattern in a string? Examples searching for a against string abcdabcd should find one occurrence at position 5 sea Jun 5, 2021 · # find index of second occurence of substring in string idx = string. May be there is a way to build a regex that fits the first occurrence of 'Name:' and a regex matching the second (or n-th) occurrence of 'Name:'. Let’s explore them. And yes, it is a duplicate; note how the top/accepted answer gives an example for the second to last element as well. ] I need to find the second largest value in that list which isn't equal to 9999. May 24, 2025 · Python Exercises, Practice and Solution: Write a Python program to find the position of the second occurrence of a given string in another given string. We would like to show you a description here but the site won’t allow us. You'll look into two different strategies, for loops and generators, and compare their performance. NumPy: the absolute basics for beginners # Welcome to the absolute beginner’s guide to NumPy! NumPy (Num erical Py thon) is an open source Python library that’s widely used in science and engineering. cgyvkuhvutknltynlqkrzmlhqaoaezhdguadkmoymquetlhmpquhpupm