Pandas Python remove elements from list with condition

Question

Suppose I have a the following list

List = ['0000', '0010', '0020', '0030', '0040', '0050', '0060', '0070']

Using Pandas python I want to remove elements from list where the 2nd last numbers is odd. I have the following code but I get an error.

for a in List:
    if [int(a[-2]) for a in List] % 2 != 0:
        List.remove(a)

Expected Output List = ['0000', '0020', '0040', '0060']

I have the following code but I get an error Saying "I got an error" isn't very useful. Show us the error. — John Gordon
– John Gordon, Commented Nov 19, 2020 at 0:51
li.remove(a) What is li? You haven't defined that variable. — John Gordon
– John Gordon, Commented Nov 19, 2020 at 0:51
Forgive me @JohnGordon it meant to say List but an answer has been supplied already. Thank you — Moshe
– Moshe, Commented Nov 19, 2020 at 0:53
I'm guessing the error was TypeError: unsupported operand type(s) for %: 'list' and 'int' since you are trying to apply % to something between brackets! — Stef
– Stef, Commented Nov 19, 2020 at 1:00

avarice · Accepted Answer · 2020-11-19 00:45:53Z

3

You are removing items from list while iterating, maybe that's the root of the problem, Try out a list comprehension

List = ['0000', '0010', '0020', '0030', '0040', '0050', '0060', '0070']

List = [x for x in List if not x[-2] in [str(z) for z in range(1,10,2)]]

print(List)

answered Nov 19, 2020 at 0:45

avarice

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3 Comments

Moshe Over a year ago

Can you you kindly help me understand ` [str(z) for z in range(1,10,2)]`?

avarice Over a year ago

That is a list comprehension to iterate over the range of 1 to 11 with step 2 and convert each iteratiom variable to str and compare

Moshe Over a year ago

In the event that I need to change the condition from ``Odd` to a list of numbers for example [6,7,8,9] am I correct to write [str(z) for z in range(6,8,1)]?

avarice · Accepted Answer · 2020-11-19 02:01:38Z

1

Since you tagged the question pandas:

out = pd.Series(List).loc[lambda x : x.str[-2].astype(int)%2==0].tolist()
Out[94]: ['0000', '0020', '0040', '0060']

edited Nov 19, 2020 at 2:01

avarice

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answered Nov 19, 2020 at 0:46

BENY

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Comments

user27637 · Accepted Answer · 2020-11-19 00:49:16Z

0

for a in List:
    if int(a[-2]) % 2 != 0:
        List.remove(a)

answered Nov 19, 2020 at 0:49

user27637

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2 Comments

Stef Over a year ago

This actually has quadratic time complexity because remove has to search for the element before removing it.

Stef Over a year ago

Suggested alternative: newlist = []; for a in List: if a[-2] in '13579': newlist.append(a).

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