How to compare 2 lists and to get True or False list in Python?

Question

Let's assume I have:

A = ['a','b','c','d','e']
B = ['a','b','e']

I want to compare this 2 lists and get smth like:

[True, True, False, False, True]

The problem which I have is that lists must have a same length. But how to compare if they aren't?

I need faster way, because I'm working with df with 98800 observations. I searched in internet, but I can not to find what I need.

Thank you

I didn't get. I know 'in' method, but I'm not sure that I understood your answer. — Pon4a, Dec 04 '18 at 09:41
what if `B` contained a unique item `'f'`? Can you describe your problem a bit better? Is the comparison based on the values in `A` exclusively? — Ma0, Dec 04 '18 at 09:41
You didn't explicitely state what the rule should be to get the output if the lists don't have the same length. Try to explain it, give sample input and output. — Thierry Lathuille, Dec 04 '18 at 09:42
And we could convert `B` to a `set` first to have better lookup time. — Matthias, Dec 04 '18 at 09:42
@Ev.Kounis sure, my bad. The concept is that 'A' is a list of all possible values(letters in an example). 'B' is a list of random letters. 'B' can not contains any uniques values, only values from 'A'. I want to get True if 'B'[i] in 'A'[i] and False if 'A'[i] not in 'B'. — Pon4a, Dec 04 '18 at 09:50
@Pon4a, are you using dataframe or list? because they are different types of objects in python. — Mox, Dec 04 '18 at 09:57
I have df(130x98800),but I thought if I save particular column to a list that would be faster. How do you think? — Pon4a, Dec 04 '18 at 10:02
@Pon4a, you don't have to convert the column to list, you can simply do df['A'].isin(df['B']) — Mox, Dec 04 '18 at 10:04
@Mox Thank you. I will try to work with df. I wrote for loop, but it tooks time for computation (but worked correct). So I will follow your advice! — Pon4a, Dec 04 '18 at 10:07

Mox · Answer 1 · 2018-12-04T09:47:25.433

2

I think what you are looking for is the isin() function from Pandas

import pandas as pd
B = ['a','b','e']
df=pd.DataFrame({'A': ['a','b','c','d','e']});
df.isin(B)

Result

    A
0   True
1   True
2   False
3   False
4   True

the series version of isin()

edited Dec 04 '18 at 09:47

answered Dec 04 '18 at 09:42

Mox

score -1 · Answer 2 · answered Dec 04 '18 at 09:43

If you want to see which elements of list A are in list B, you can do this:

result = [x in B for x in A]

this is called list comprehension.

This is equivalent to:

result = []
for x in A:
    if x in B:
       result.append(True)
    else:
       result.append(False)

2 Answers2