Test if every element of an array is in another array

Question

Suppose I have two arrays, x and y, where y is a subset of x:

x = [1, 2, 3, 4, 5, 6, 7, 8, 9]
y = [3, 4, 7]

I want to return an array like:

ret = [False, False, True, True, False, False, True, False, False]

If y were just a single number it would be easy enough (x == y), but I tried the equivalent x in y and it didn't work. Of course, I could do it with a for loop, but I'd rather there was a neater way.

I've tagged this Pandas since x is actually a Pandas series (a column in a dataframe). y is a list, but can be made to be a NumPy array or Series if needed.

Since you tagged pandas, I've closed as a duplicate. – cs95 Mar 06 '18 at 16:14 — cs95, Mar 06 '18 at 16:14

score 3 · Answer 1 · answered Mar 06 '18 at 16:12

3

x = [1, 2, 3, 4, 5, 6, 7, 8, 9]
y = [3, 4, 7]
print([x in y for x in x])

answered Mar 06 '18 at 16:12

fourmajor

51
5

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(ab)using `x` like that (`for x in x`) is not recommended. There are many more letters to choose from. xD – Ma0 Mar 06 '18 at 16:13
@Ev.Kounis I like it. "(ab)using". Nice! – Scott Boston Mar 06 '18 at 16:14

score 3 · Answer 2 · answered Mar 06 '18 at 16:12

IIUC:

s = pd.Series(x)
s.isin(y)

Output:

0    False
1    False
2     True
3     True
4    False
5    False
6     True
7    False
8    False
dtype: bool

And to return list:

s.isin(y).tolist()

Output:

[False, False, True, True, False, False, True, False, False]

score 0 · Answer 3 · answered Mar 06 '18 at 16:29

0

Set Intersection can also do this for you.

a = [1,2,3,4,5,9,11,15]
b = [4,5,6,7,8]
c = [True if x in list(set(a).intersection(b)) else False for x in a]

print(c)

answered Mar 06 '18 at 16:29

eatmeimadanish

3,809
1
14
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Test if every element of an array is in another array

3 Answers3