# Calculate harmonic mean in Python (with examples)

Harmonic mean (HM) is defined as a **reciprocal of** * the arithmetic mean of the reciprocal of given numbers*.

There should be no zero number in the dataset, otherwise harmonic mean will be zero. The harmonic mean is commonly used for calculating the mean of rates or ratios (e.g. speed of the car) as it gives more accurate answers than arithmetic means.

### Calculate harmonic mean in Python

**Example**: The speed of three cars are 20 mph, 40 mph, and 80 mph. Calculate the harmonic mean of the cars
speed.

You can calculate the harmonic mean of the speed of cars using the `hmean()`

function available in the `scipy`

package. `hmean() `

function takes the following arguments,

** a**: input array of numbers

```
from scipy.stats import hmean
hmean(a = [20, 40, 80])
# output
34.2857
```

The harmonic mean of the speed of three cars is 34.2857 mph.

### Calculate harmonic mean from scratch in Python

First, calculate the arithmetic mean of the reciprocal of given non-zero numbers,

```
import numpy as np
m = np.mean([1/20, 1/40, 1/80])
```

Now, get the reciprocal of the arithmetic mean,

```
hm = 1/m
hm
# output
34.2857
```

The harmonic mean of the speed of three cars is 34.2857 mph.

## Enhance your skills with courses on Statistics and Python

- Introduction to Statistics
- Python for Everybody Specialization
- Python 3 Programming Specialization
- Statistics with Python Specialization
- Advanced Statistics for Data Science Specialization

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