np.setdiff1d() for difference in NumPy - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does np.setdiff1d() do in NumPy?

np.setdiff1d() returns the sorted, unique values in one array that are not in another array. It finds the difference between two arrays.

beginner

How does np.setdiff1d() handle duplicate values in the input arrays?

It removes duplicates and returns only unique values from the first array that are not in the second array.

beginner

Example: What is the output of np.setdiff1d([1, 2, 3, 4], [2, 4])?

The output is [1 3] because 1 and 3 are in the first array but not in the second.

intermediate

Can np.setdiff1d() be used with arrays of strings?

Yes, it works with any array of comparable elements, including strings, returning unique elements from the first array not in the second.

intermediate

Why is the output of np.setdiff1d() always sorted?

Because np.setdiff1d() sorts the unique values before returning them to provide consistent and predictable output.

What does np.setdiff1d(a, b) return?

A All elements from both arrays combined

B Elements in <code>b</code> not in <code>a</code>

C Common elements in both <code>a</code> and <code>b</code>

D Elements in <code>a</code> not in <code>b</code>

np.setdiff1d(a, b) returns elements that are in a but not in b.

If a = [1, 2, 2, 3] and b = [2], what does np.setdiff1d(a, b) return?

A [1, 3]

B [1, 2, 3]

C [2]

D [3]

Duplicates are removed, so only unique elements in a not in b are returned: 1 and 3.

Is the output of np.setdiff1d() always sorted?

A Yes

B No

C Only if arrays are sorted

D Depends on input type

The function always returns sorted unique values for consistency.

Can np.setdiff1d() be used with string arrays?

A Only with boolean arrays

B Yes

C Only with numeric arrays

D No

It works with any comparable data type, including strings.

What happens if all elements of a are in b when using np.setdiff1d(a, b)?

A Returns <code>a</code> unchanged

B Returns <code>b</code>

C Returns an empty array

D Raises an error

If no elements in a are unique compared to b, the result is an empty array.

Explain how np.setdiff1d() works and give a simple example.

Think about finding what is left in one list after removing items found in another.

Describe a real-life situation where you might use np.setdiff1d().

Imagine you have two lists and want to find what is only in one of them.