Coding Grandmaster · project 30 of 46 · premium, free for now

Scaling and z-scores

Write min_max(values) and z_scores(values) (use the population standard deviation). Both return lists with each number rounded to 2 decimal places.

Learn

To compare things measured on different scales, put them on a common one. Min-max scaling squeezes values into 0 to 1: (v − min) ÷ (max − min). A z-score says how many standard deviations a value is from the mean: (v − mean) ÷ std. A z-score of +2 is unusually high, and the z-scores of any list always average to 0.

Your task

Write min_max(values) and z_scores(values) (use the population standard deviation). Both return lists with each number rounded to 2 decimal places.

Stretch challenge

Use z-scores to find which of two students did better, one scoring 78 in a hard test and one 85 in an easy one.

← Do two things move together?Records, filters and rankings →

Python

Press Run to see what your program prints.

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Averages

Write mean(data), median(data) and mode(data). If several values tie for most common, mode returns the smallest of them. Print all three for the list.

Start →26

How spread out?

Write data_range(data), variance(data) and std_dev(data) (population versions, dividing by n). Print them for the data, rounding the standard deviation to 4 decimal places.

Start →27

Quartiles and outliers

Write quartiles(data) returning (q1, q2, q3) by the method above, and outliers(data) returning the sorted list of outliers by the 1.5 × IQR rule.

Start →28

A histogram in text

Count how many students got each grade and print one line per grade in alphabetical order, like A | #### 4.

Start →29

Do two things move together?

Write correlation(xs, ys) that returns Pearson's r rounded to 4 decimal places. Print it for study hours against marks.

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Practise the idea

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FAQ

Scaling and z-scores: common questions

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