Data Science with Python Certification Data Analysis with Python 4

Question 1

Which pandas merge type returns only rows that have matching keys in both DataFrames?

Accepted Answer

inner

Answer

An inner join (how='inner') keeps only the intersection — rows whose keys exist in both DataFrames.

Question 2

What does df.rolling(window=7).mean() compute?

Accepted Answer

The 7-period simple moving average for each column

Answer

rolling(7).mean() calculates a sliding 7-observation window average, shifting one row at a time.

Question 3

Which method detects duplicate rows in a pandas DataFrame and returns a boolean Series?

Accepted Answer

df.duplicated()

Answer

df.duplicated() returns True for each row that is an exact duplicate of an earlier row.

Question 4

What is the output dtype of np.array([1, 2.0, 3])?

Accepted Answer

float64

Answer

NumPy upcasts the entire array to float64 because 2.0 is a float and int is a subtype of float.

Question 5

Which pandas accessor is used to perform string operations on a Series of strings?

Accepted Answer

.str

Answer

The .str accessor exposes vectorized string functions like .str.upper(), .str.split(), and .str.replace().

Data Science with Python Certification Practice Test