# Python Data Visualisation for Business Analyst – How to do Box Plot in Python

In this data visualisation tutorial, you will learn How to do Box Plot in Python.

Box plots are a great way to visualize the distribution, keeping the median, 25th 75th quartiles and the outliers in mind. However, you need to be careful about interpreting the size the boxes which can potentially distort the number of points contained within that group. So, manually providing the number of observations in each box can help overcome this drawback.

For example, the first two boxes on the left have boxes of the same size even though they have 5 and 47 obs respectively. So writing the number of observations in that group becomes necessary.

## Setup

Run this once before the plot’s code. The individual charts, however, may redefine its own aesthetics.

/* !pip install brewer2mpl */
import numpy as np
import pandas as pd
import matplotlib as mpl
import matplotlib.pyplot as plt
import seaborn as sns
import warnings; warnings.filterwarnings(action='once')

large = 22; med = 16; small = 12
params = {'axes.titlesize': large,
'legend.fontsize': med,
'figure.figsize': (16, 10),
'axes.labelsize': med,
'axes.titlesize': med,
'xtick.labelsize': med,
'ytick.labelsize': med,
'figure.titlesize': large}
plt.rcParams.update(params)
plt.style.use('seaborn-whitegrid')
sns.set_style("white")
%matplotlib inline

/* Version */
print(mpl.__version__)
print(sns.__version__)

## How to do Box plot in Python

/* Import Data */

/* Draw Plot */
plt.figure(figsize=(13,10), dpi= 80)
sns.boxplot(x='class', y='hwy', data=df, notch=False)

/* Add N Obs inside boxplot (optional) */
medians_dict = {grp[0]:grp[1][y].median() for grp in df.groupby(group_col)}
xticklabels = [x.get_text() for x in plt.gca().get_xticklabels()]
n_obs = df.groupby(group_col)[y].size().values
for (x, xticklabel), n_ob in zip(enumerate(xticklabels), n_obs):
plt.text(x, medians_dict[xticklabel]*1.01, "#obs : "+str(n_ob), horizontalalignment='center', fontdict={'size':14}, color='white')

/* Decoration */
plt.title('Box Plot of Highway Mileage by Vehicle Class', fontsize=22)
plt.ylim(10, 40)
plt.show()

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