WAP to remove duplicates in a list. Why is this wrong?-CodePudding

I expected every element to go through the for loop, then the duplicate ones to be removed through the if loop.

num = [5, 7, 21, 7, 5, 7, 7, 5, 7 , 7]

for i in num:
    if num.count(i)!=1:

        num.remove(i)

print(num)

CodePudding user response：

Since you are reducing the size of array while iterating on it. for i in num will check for the length of num. After 5 iterations (i=5), the length of num will become 5 and the loop will break.

It's better to always avoid mutating the list you're looping on.

Same result can also be achieved simply by:

num = list(set(num))

CodePudding user response：

list. remove(object) Removes the first item from the list which matches the specified value.

To solve your purpose we can utilize a data structure name set which have property to store multiple items in a single variable.

num = [5, 7, 21, 7, 5, 7, 7, 5, 7 , 7]
print(set(num))

If you want to go with your logic instead of using set data structure checkout this code

num = [5, 7, 21, 7, 5, 7, 7, 5, 7 , 7]

res = []
for i in range(len(num)):
    if num.index(num[i])==i:
        res.append(num[i])

print(res)

num = [5, 7, 21, 7, 5, 7, 7, 5, 7 , 7]

res = []
for i in num:
    if i not in res:
        res.append(i)

print(res)

CodePudding user response：

Why not use np.unique?

import numpy as np
unique_num = np.unique(num)

https://numpy.org/doc/stable/reference/generated/numpy.unique.html