Python | Indices of numbers greater than K

Many times we might have problem in which we need to find indices rather than the actual numbers and more often, the result is conditioned. First approach coming to mind can be a simple index function and get indices greater than particular number, but this approach fails in case of duplicate numbers. Let’s discuss certain ways in which this problem can be successfully solved.

Method #1 : Using loop
This problem can easily be solved using loop with a brute force approach in which we can just check for the index as we iterate and append it in a new list as we proceed forward.

# Python3 code to demonstrate 
# index of matching element using loop 
  
# initializing list  
test_list = [12, 10, 18, 15, 8, 18] 
  
# printing original list 
print("The original list : " + str(test_list)) 
  
# using loop 
# index of matching element 
res = [] 
for idx in range(0, len(test_list)) : 
    if test_list[idx] > 10: 
        res.append(idx) 
  
# print result 
print("The list of indices greater than 10 : " + str(res)) 

Output :

The original list : [12, 10, 18, 15, 8, 18]
The list of indices greater than 10 : [0, 2, 3, 5]

Method #2 : Using list comprehension + enumerate()
The combination of these two function can also perform this particular task efficiently and in one line. The enumerate function is used to get element and its index simultaneously.

# Python3 code to demonstrate 
# index of matching element 
# using list comprehension + enumerate() 
  
# initializing list  
test_list = [12, 10, 18, 15, 8, 18] 
  
# printing original list 
print("The original list : " + str(test_list)) 
  
# using list comprehension + enumerate() 
# index of matching element 
res = [idx for idx, val in enumerate(test_list) if val > 10] 
  
# print result 
print("The list of indices greater than 10 : " + str(res)) 

Output :

The original list : [12, 10, 18, 15, 8, 18]
The list of indices greater than 10 : [0, 2, 3, 5]

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