pct_change() for percentage change in Pandas - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the pct_change() function in pandas do?

It calculates the percentage change between the current and a prior element in a pandas Series or DataFrame. This helps to see how much values have increased or decreased in percentage terms.

beginner

How do you calculate the percentage change between rows in a DataFrame using pandas?

Use df.pct_change(). By default, it calculates the percentage change between the current row and the previous row for each column.

intermediate

What does the periods parameter in pct_change() control?

It controls how many rows (or periods) back to compare the current value to. For example, periods=2 compares the current row to the row two steps before.

intermediate

If a value in the previous row is zero, what will pct_change() return for that row?

It will return inf (infinity) or NaN because division by zero is undefined in percentage change calculation.

intermediate

How can you use pct_change() to calculate monthly percentage changes in a time series DataFrame?

Set the DataFrame index to a datetime type and use df.pct_change(periods=1) if data is monthly. For other frequencies, adjust periods accordingly.

What is the default number of periods pct_change() compares when calculating percentage change?

A 0

B 1

C 2

D -1

By default, pct_change() compares the current row with the previous row, which means periods=1.

If a DataFrame column has values [100, 110, 121], what is the percentage change from the first to the second value?

A 10%

B 11%

C 21%

D 1%

Percentage change = (110 - 100) / 100 = 0.10 or 10%.

What will pct_change() return if the previous value is zero?

A NaN or infinity

B Negative value

C Zero

D Previous value

Division by zero is undefined, so pandas returns NaN or infinity.

Which pandas object can use pct_change()?

A Series only

B DataFrame only

C Both Series and DataFrame

D Neither

pct_change() works on both Series and DataFrame objects.

How do you calculate percentage change comparing to two rows before in pandas?

A df.pct_change(periods=1)

B df.pct_change(periods=-2)

C df.pct_change(periods=0)

D df.pct_change(periods=2)

Setting periods=2 compares the current row to the row two steps before.

Explain how the pct_change() function works in pandas and give an example of when you might use it.

Think about comparing current and previous values to see growth or decline.

Describe how you would handle a situation where the previous value is zero when using pct_change().

Consider what happens mathematically when dividing by zero.