Data Science with Python Pandas DataFrame Operations Flashcards
7 cards from real Data Science with Python Certification practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
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Which method returns the number of non-null values in each column of a DataFrame?
Answer: df.count()
df.count() returns the count of non-null values per column by default.
What does df.pivot_table(values='sales', index='region', aggfunc='mean') compute?
Answer: Mean sales per region
The aggfunc='mean' parameter computes the average of the 'sales' column grouped by 'region'.
How do you rename columns 'a' and 'b' to 'x' and 'y' in a DataFrame df?
Answer: df.rename(columns={'a':'x','b':'y'})
df.rename(columns={...}) accepts a mapping dict via the columns keyword argument.
What is the result of df.duplicated() on a DataFrame?
Answer: Returns a boolean Series marking duplicate rows
df.duplicated() returns a boolean Series where True indicates a row is a duplicate of a previous row.
Which of the following correctly filters rows where column 'age' is between 18 and 35 (inclusive)?
Answer: df[df['age'].between(18, 35)]
The .between(left, right) method returns True for values within the inclusive range.
What does df.melt(id_vars=['id'], value_vars=['q1','q2']) do?
Answer: Transforms wide data to long format
df.melt() unpivots a DataFrame from wide to long format, keeping id_vars fixed and stacking value_vars.
How do you compute a rolling 7-day mean on column 'price' in a DataFrame df?
Answer: df['price'].rolling(7).mean()
rolling(7).mean() computes a sliding window average over 7 consecutive observations.
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