We can get the index of an element in a list using the .index()
function.
I was wondering if there's any better way to find the index without using the built-in function (of list).
Currently, I have written the following code using enumerate
:
x = int(input("Enter a number to get the index:"))
l = [3,11,4,9,1,23,5]
if x in l: # I think this line is unnecessary and is increasing the time.
for i, val in enumerate(l):
#Instead checking for x above can i use
#if x == val: Don't worry about the indentation I'll fix it.
print(f"Index of {x} is {i}.")
else:
print("Item not found.")
So, is there a better way(in terms of time taken) to accomplish this? Thanks for your time and knowledge.
CodePudding user response:
use list comprehension in python
l = [3, 11, 4, 9, 1, 23, 5, 11]
indexes = [index for index in range(len(l)) if l[index] == 11]
output:
[1, 7]
use numpy
for finding the matching indices.
l = [3, 11, 4, 9, 1, 23, 5, 11]
np_array = np.array(l)
item_index = np.where(np_array == 11)
print (item_index)
Numpy is efficient:
import random
import time
import numpy as np
limit = 10 ** 7
l = [None] * limit
for i in range(limit):
l[i] = random.randint(0, 1000000)
start = time.time()
np_array = np.array(l)
item_index = np.where(np_array == 11)
print('time taken by numpy', time.time() - start)
start = time.time()
for index, value in enumerate(l):
if (value == 11):
pass
print('time taken by enumerate',time.time() - start)
Output:
time taken by numpy 0.9375550746917725
time taken by enumerate 1.4508612155914307