Python list get element by value

Get first element in List that matches condition in Python

This tutorial will discuss about unique ways to get first element in list that matches condition in Python.

Table Of Contents

Introduction

We have a list of numbers, and we want to get the first odd number from that list. Basically, we want to fetch the first element from list that satisfies out condition.

The condition is :
* Number should be Odd i.e. if we divide it by two then reminder should be 1,

Method 1: Using next() method

Use a Generator expression to yield only those elements from list that satisfies a given condition i.e. only odd numbers. Basically, it will return us a generator object. Then pass that generator object to the next() function in Python, along with a default value None. The next() method, will return the first item from generator object i.e. first odd number from list. If there is no item in list that satisfies the given condition i.e. no odd number in list, then it will return None . So, in the below example, either it will return None or the first odd number from list.

Frequently Asked:

Let’s see the complete example,

listOfNumbers = [12, 42, 44, 68, 91, 72, 71, 81, 82] # Get first item in list that matches a condition e.g. # Get first odd value from the list value = next( (elem for elem in listOfNumbers if elem % 2 == 1), None) print(value)

Method 2: Using for-loop

Iterate over the list using a for-loop, and for each element check if satisfies the given condition or not. If yes, then stop the loop and return the current value.

In the below example, our condition is that the number should be odd. So, it will return the first odd number from list.

Let’s see the complete example,

listOfNumbers = [12, 42, 44, 68, 91, 72, 71, 81, 82] value = None # Get first item in list that matches a condition e.g. # get first odd value from the list for elem in listOfNumbers: if elem % 2 == 1: value = elem break print (value)

Method 3: Using any() method

The any() method accepts an iterable sequence as an argument and reurns True as soon as any element in that sequence evaluates to True.

So, iterate over all elements of List in a generator expression, and check the given condition on each element. While iterating store each element in variable “value”. As soon as any element satisfies the condition, it will evaluate to True for that element. The any() method will return True at that point. The variable “value” will have the value for which any() method returned True .

In the below example, our condition is that the number should be a odd number. So, it will fetch the first odd number from list, or if list does not have any odd number then it will give None .

Let’s see the complete example,

listOfNumbers = [12, 42, 44, 68, 91, 72, 71, 81, 82] # Get first item in list that matches a condition e.g. # get first odd value from the list if not any((value := elem) % 2 == 1 for elem in listOfNumbers): value = None print (value)

Summary

We learned about different ways to access the first element in list that matches the given condition in Python.

Related posts:

Share your love

Leave a Comment Cancel Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.

Terms of Use

Disclaimer

Copyright © 2023 thisPointer

To provide the best experiences, we and our partners use technologies like cookies to store and/or access device information. Consenting to these technologies will allow us and our partners to process personal data such as browsing behavior or unique IDs on this site and show (non-) personalized ads. Not consenting or withdrawing consent, may adversely affect certain features and functions.

Click below to consent to the above or make granular choices. Your choices will be applied to this site only. You can change your settings at any time, including withdrawing your consent, by using the toggles on the Cookie Policy, or by clicking on the manage consent button at the bottom of the screen.

The technical storage or access is strictly necessary for the legitimate purpose of enabling the use of a specific service explicitly requested by the subscriber or user, or for the sole purpose of carrying out the transmission of a communication over an electronic communications network.

The technical storage or access is necessary for the legitimate purpose of storing preferences that are not requested by the subscriber or user.

The technical storage or access that is used exclusively for statistical purposes. The technical storage or access that is used exclusively for anonymous statistical purposes. Without a subpoena, voluntary compliance on the part of your Internet Service Provider, or additional records from a third party, information stored or retrieved for this purpose alone cannot usually be used to identify you.

The technical storage or access is required to create user profiles to send advertising, or to track the user on a website or across several websites for similar marketing purposes.

Источник

5 Easy Ways To Extract Elements From A Python List

Let’s learn the different ways to extract elements from a Python list When more than one item is required to be stored in a single variable in Python, we need to use lists. It is one of python’s built-in data functions. It is created by using [ ] brackets while initializing a variable.

In this article, we are going to see the different ways through which lists can be created and also learn the different ways through which elements from a list in python can be extracted.

1. Extract Elements From A Python List Using Index

Here in this first example, we created a list named ‘firstgrid’ with 6 elements in it. The print statement prints the ‘1’ element in the index.

firstgrid=["A","B","C","D","E","F"] print(firstgrid[1])

2. Print Items From a List Using Enumerate

Here, we created a variable named ‘vara’ and we filled the elements into the list. Then we used ‘varx’ variable to specify the enumerate function to search for ‘1,2,5’ index positions.

vara=["10","11","12","13","14","15"] print([varx[1] for varx in enumerate(vara) if varx[0] in [1,2,5]])

3. Using Loops to Extract List Elements

You can also Extract Elements From A Python List using loops. Let’s see 3 methods to pull individual elements from a list using loops.

Method 1:

Directly using a loop to search for specified indexes.

vara=["10","11","12","13","14","15"] print([vara[i] for i in (1,2,5)])

Method 2:

Storing list and index positions into two different variables and then running the loop to search for those index positions.

elements = [10, 11, 12, 13, 14, 15] indices = (1,1,2,1,5) result_list = [elements[i] for i in indices] print(result_list)

Method 3:

In this example, we used a different way to create our list. The range function creates a list containing numbers serially with 6 elements in it from 10 to 15.

numbers = range(10, 16) indices = (1, 1, 2, 1, 5) result = [numbers[i] for i in indices] print(result)

4. Using Numpy To View Items From a List

We can also use the popular NumPy library to help us Extract Elements From A Python List. Let’s see how that can be done here using two different methods.

Method 1:

Here, we used the numpy import function to print the index specified in variable ‘sx’ from the elements present in list ‘ax’ using np.array library function.

ax = [10, 11, 12, 13, 14, 15]; sx = [1, 2, 5] ; import numpy as np print(list(np.array(ax)[sx]))

Method 2:

This example uses variable storing index positions and another variable storing numbers in an array. The print statement prints the index positions stored in variable ‘sx’ with respect to a variable containing the list – ‘ay’.

sx = [1, 2, 5]; ay = np.array([10, 11, 12, 13, 14, 15]) print(ay[sx])

5. Extract Elements Using The index function

vara=["10","11","12","13","14","15"] print([vara[index] for index in (1,2,5,20) if 0 

Conclusion
This article explains in great detail the different methods available to search and extract elements from a python list. We learned in this article, how lists are made, the different types of python functions through which elements are extracted from the list. It is hoped that this article might have helped you.
Источник
Python list get element by value
In this article we are going to find a way to search an element from a list without using the 'in' method. A list is a data structure in Python that is changeable, ordered sequence of elements. Each element or value which is inside the list is called as item. Lists are defined by having values between square brackets '[ ]'.
In our program we first create a list with different items in it. After that we ask the user to input the item name to be searched from the list using the input() method. In the same line after input() we use lower() method so that even if the user gives input in uppercase letters our program won't throw a garbage result.
We will now create a function 'Search' to search the item given by the user. To search the item we will iterate through each element in the list and check whether item is equal to the element. If element at any index matches our item then our program will print "item found at index x." where item will be replaced by the item name given by user and x will be replaced by the index number at which we found our item. Else our program will print "item is not at index x."where item will be replaced by item name and x will be replaced by index number. In the end we'll call our function and pass the values.
#! /usr/bin/env python3 # searchList.py : Finds an element in a list without using 'in' method. # List breakFast = [ 'bread' , 'butter' , 'jam' ] # Take input from user to search the element. element = input( "Enter the element to be searched: " ).lower() # Find if the element exists in the given list. def Search (alist,elem) : for i in range(len(breakFast)): if alist[i] == elem: print(elem + " found at index " + str(i)) break else : # only executes if loop finishes without break. print(elem + " is not at index " + str(i)) # call the function and pass the values. Search(breakFast,element) 
Источник