Question

How to find the indexes of all the occurrences of element in a list with Python

Answer 1

import numpy as np

lst = [43, 21, 67, 21, 30, 18, 21, 19, 21, 21]

lst = np.array(lst)

result = np.where(lst == 21)

print(result)
print(result[0])

     
 
'''
run:
 
(array([1, 3, 6, 8, 9]),)
[1 3 6 8 9]
 
'''

 

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Answer 2

lst = [43, 21, 67, 21, 30, 18, 21, 19, 21, 21]
 
pos = []
n = 21

for i in range(len(lst)):
    if lst[i] == n:
        pos.append(i)
        
print(pos)
 
 
      
  
'''
run:
  
[1, 3, 6, 8, 9]
  
'''

 

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Answer 3

lst = [43, 21, 67, 21, 30, 18, 21, 19, 21, 21]
 
n = 21

pos = [i for i in range(len(lst)) if lst[i] == n]

print(pos)
 
      
      
  
'''
run:
  
[1, 3, 6, 8, 9]
  
'''

 

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Answer 4

lst = [43, 21, 67, 21, 30, 18, 21, 19, 21, 21]
 
n = 21

pos = [i for i, x in enumerate(lst) if x == n]

print(pos)
 
      
      
  
'''
run:
  
[1, 3, 6, 8, 9]
  
'''

 

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Answer 5

import numpy as np
 
lst = [43, 21, 67, 21, 30, 18, 21, 19, 21, 21]
 
n = 21
 
result = np.where(np.array(lst) == n)[0]
 
print(result)

    
      
  
'''
run:
  
[1 3 6 8 9]
  
'''

 

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Answer 6

from more_itertools import locate
 
lst = [43, 21, 67, 21, 30, 18, 21, 19, 21, 21]
 
n = 21
 
result = list(locate(lst, lambda x: x == n))
 
print(result)

    
      
  
'''
run:
  
[1 3 6 8 9]
  
'''

 

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