Error in Final Exam of C2_W4

Course Q&A Machine Learning Specialization Advanced Learning Algorithms
1

Hi, I’m getting errors from the unittest (see below) in this exam although the code seems to be yielding the expected output, could you please help? thanks,

ERROR:

Information Gain from splitting the root on brown cap: 0.034851554559677034
Information Gain from splitting the root on tapering stalk shape: 0.12451124978365313
Information Gain from splitting the root on solitary: 0.2780719051126377

AssertionError Traceback (most recent call last)
in
9
10 # UNIT TESTS
—> 11 compute_information_gain_test(compute_information_gain)

~/work/public_tests.py in compute_information_gain_test(target)
113
114 result = target(X, y, node_indexes, 1)
→ 115 assert np.isclose(result, 0, atol=1e-6), f"Wrong information gain. Expected {0.0} got: {result}"
116
117 print(“\033[92m All tests passed.”)

AssertionError: Wrong information gain. Expected 0.0 got: nan

There is nothing apparently wrong with my code, can someone please help? thanks

2

Hi Napolean!

If we look at the failed test we can see that the function is producing a nan.
What is nan and how is it produced?

One way is division by 0.
After nan has been produced any arithmetic with nan is nan.

I would check everywhere division is performed in compute_information_gain() and compute_entropy() for where division by 0 can occur and try to prevent it.

Hope this helps!

3

Thanks for your help, this was indeed the issue, I managed to resolve it upon further inspection.

4

Information Gain from splitting the root on brown cap: 0.034851554559677034
Information Gain from splitting the root on tapering stalk shape: 0.12451124978365313
Information Gain from splitting the root on solitary: 0.2780719051126377

AssertionError Traceback (most recent call last)
in
9
10 # UNIT TESTS
—> 11 compute_information_gain_test(compute_information_gain)

~/work/public_tests.py in compute_information_gain_test(target)
113
114 result = target(X, y, node_indexes, 1)
→ 115 assert np.isclose(result, 0, atol=1e-6), f"Wrong information gain. Expected {0.0} got: {result}"
116
117 print(“\033[92m All tests passed.”)

AssertionError: Wrong information gain. Expected 0.0 got: nan

5

“nan” means your code is not computing a real-valued result. “nan” means “not a number”.