Percentiles with np.percentile() in NumPy - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a percentile in data analysis?

A percentile is a value below which a certain percentage of data falls. For example, the 25th percentile is the value below which 25% of the data lies.

beginner

What does the function np.percentile() do?

np.percentile() calculates the value below which a given percentage of data in an array falls. It helps find specific percentiles like median (50th percentile) or quartiles.

beginner

How do you find the median of an array arr using np.percentile()?

Use np.percentile(arr, 50). The 50th percentile is the median, the middle value of the data.

intermediate

What is the difference between the 25th and 75th percentiles?

The 25th percentile (Q1) is the value below which 25% of data falls, and the 75th percentile (Q3) is the value below which 75% of data falls. The difference between them is called the interquartile range (IQR), showing data spread.

intermediate

How does np.percentile() handle multi-dimensional arrays?

np.percentile() can calculate percentiles along a specified axis using the axis parameter. This lets you find percentiles for rows or columns separately.

What does np.percentile(arr, 90) return?

A The average of the data in <code>arr</code>

B The value below which 90% of the data in <code>arr</code> falls

C The maximum value in <code>arr</code>

D The value above which 90% of the data falls

np.percentile(arr, 90) returns the 90th percentile, meaning 90% of data is below this value.

Which percentile corresponds to the median?

A 50th percentile

B 25th percentile

C 75th percentile

D 100th percentile

The median is the 50th percentile, the middle value of the data.

How do you calculate the interquartile range (IQR) using percentiles?

A 50th percentile minus 25th percentile

B Maximum minus minimum

C 75th percentile minus 25th percentile

D 25th percentile plus 75th percentile

IQR = Q3 (75th percentile) - Q1 (25th percentile), showing the middle 50% spread.

What parameter do you use in np.percentile() to calculate percentiles along columns of a 2D array?

A axis=2

B axis=1

C axis=None

D axis=0

Use axis=0 to calculate percentiles down columns (each column separately).

If you want the 0th percentile of data, what value does np.percentile() return?

A Minimum value

B Maximum value

C Mean value

D Median value

The 0th percentile is the smallest value in the data.

Explain what a percentile is and how you can use np.percentile() to find the median and quartiles in a dataset.

Think about how percentiles split data into parts and how np.percentile helps find those split points.

Describe how to calculate the interquartile range (IQR) using np.percentile() and why it is useful.

IQR is the difference between two key percentiles that capture the middle half of data.