Visualization Matplotlib

In this section, we’ll use matplotlib.pyplot, which has been imported and used (aliased) as plt.

import matplotlib.pyplot as plt

Scatterplot

• For a single point, provide (x_coordinate, y-coordinate).

• For multiple points, provide (x_coordinate sequence, y-coordinate sequence), where the sequence can be a tuple, list, or series.

# single point
plt.scatter(5,10);    # x=5, y=10

If multiple points are given with their coordinates as follows:

• x_coordinate sequence: [2, 4, 5]

• y_coordinate sequence: [10, 3, 6]

• In this setup:

  • 2 corresponds to the x-coordinate of the first point, and 10 corresponds to its y-coordinate.

  • 4 corresponds to the x-coordinate of the second point, and 3 corresponds to its y-coordinate.

  • 5 corresponds to the x-coordinate of the third point, and 6 corresponds to its y-coordinate.

In the following code, the points are: \((2,10), (4,3), (5,6)\).

# multiple points
plt.scatter([2,4,5],[10,3,6]);  

Figure Size

The size of a chart figure can be adjusted using the figsize=(width, height) parameter of plt.figure().

plt.figure(figsize=(10,3))    # width:10, height:3
plt.scatter([2,4,5],[10,3,6]);    

Color

The c or color parameter is used to modify the color of points (markers).

plt.scatter([2,4,5],[10,3,6], c='red');    # instead of 'red' it is enough to write 'r' 

plt.scatter([2,4,5],[10,3,6], color='r');    # color parameter

Size

The s is used to modify the size of points (markers).

plt.scatter([2,4,5],[10,3,6], s=300);    # size=300

Markers and Scatters

The marker parameter is used to modify the style of points (markers).

For more marker styles check:

• https://matplotlib.org/stable/api/markers_api.html#module-matplotlib.markers

# plus symbol
plt.scatter([2,4,5],[10,3,6], marker='+');

# square
plt.scatter([2,4,5],[10,3,6], marker='s');

Transparency

The alpha parameter is used to modify the transparency of points (markers).

• alpha is a number between 0 (transparent) and 1 (opaque).

plt.scatter([2,4,5],[10,3,6], alpha=0.3);

Linewidth and Scatters

The linewidth and edgecolor parameters are used to modify the boundary of points (markers).

plt.scatter([2,4,5],[10,3,6], c='r', s=200, linewidths=5, edgecolor='b');

Title

The plt.title() is used to add a title to the figure.

plt.title('Three Square Points')
plt.scatter([2,4,5],[10,3,6], c='r', s=200, marker='s');

# pad adds a padding below the title
# fontsize and location (loc) can be modified.

plt.title('Three Points', fontsize=20, loc='right', pad=100, c='b')
plt.scatter([2,4,5],[10,3,6], c='r', s=200, marker='s');

Suptitle

The plt.suptitle() is used to add a suptitle to the figure.

plt.title('Three Points', fontsize=20, loc='right', pad=100, c='b')
plt.suptitle('Different Colors', fontsize=15, c='g', y=1)
plt.scatter([2,4,5],[10,3,6], c='r', s=200, marker='s');

Grid

The plt.grid() is used to add horizontal and vertical grids to the figure.

plt.scatter([2,4,5],[10,3,6])
plt.grid();

# only vertical
plt.scatter([2,4,5],[10,3,6])
plt.grid(axis='x');

# only horizontal
plt.scatter([2,4,5],[10,3,6])
plt.grid(axis='y');

Legend

The plt.legend() is used to add a legend to the figure.

plt.scatter([2,4,5],[10,3,6], c='r', label='reds')
plt.scatter([5,1,9],[4,8,7],  c='g', label='greens')
plt.legend();

# location of legend: lower left

plt.scatter([2,4,5],[10,3,6], c='r', label='reds')
plt.scatter([5,1,9],[4,8,7],  c='g', label='greens')
plt.legend(loc='lower left');

Axis Labels

The plt.xlabel() and plt.ylabel() are used to add x-axis and y-axis labels to the figure.

plt.scatter([2,4,5],[10,3,6])
plt.xlabel('x_coordiante')
plt.ylabel('y_coordiante');

Axis Ticks

The plt.xticks() and plt.yticks() are used to modify the ticks of both the x and y axes, respectively.

plt.scatter([2,4,5],[10,3,6])
plt.xticks([2,4,5], ['Washington', 'Alabama','Virginia']);

# rotation
plt.scatter([2,4,5],[10,3,6])
plt.xticks([2,4,5], ['Washington', 'Alabama','Virginia'], rotation=90);

Text

The plt.text()is used to add a text starting from the specified coordinate on the figure.

plt.scatter([2,4,5],[10,3,6])
plt.text(4.05,3,'Alabama');   # starts from the point (4.05,3)

Facecolor

The facecolor of a chart figure can be adjusted using the facecolor parameter of plt.figure().

plt.figure(facecolor='g')
plt.scatter([2,4,5],[10,3,6]);

# background of the figure
plt.axes().set_facecolor('yellow')
plt.scatter([2,4,5],[10,3,6]);

Subplot

plt.subplot() is used to create multiple plots within a single figure. Here’s a breakdown of its parameters:

• The first parameter specifies the number of rows of subplots.

• The second parameter specifies the number of columns of subplots.

• The third parameter specifies the order of the subplot, starting from 1 and increasing row-wise and then column-wise.

# number of rows: 1
# number of columns: 3

plt.figure(figsize=(20,5))
plt.subplot(1,3,1)
plt.scatter([2,4],[8,7],c='r')
plt.subplot(1,3,2)
plt.scatter([1,2],[5,12],c='b')
plt.subplot(1,3,3)
plt.scatter([6,10],[1,2],c='g');

Lineplot

plt.plot() creates a line plot by connecting the given points using line segments.

plt.plot([1,3],[7,10]);  # start from (1,3) up to (3,10)

Linewidth and Lines

The linewidth is used to modify the width of the line.

plt.plot([1,3],[7,10], linewidth=7);

Color and Lines

The c or color parameter is used to modify the color of the line.

plt.plot([1,3],[7,10], c='r');

Linestyle and Lines

The linestyle parameter is used to modify the style of the line.

plt.plot([1,7],[3,10], c='r', linestyle='dashed')
plt.plot([0,8],[12,3], c='g', linestyle='dotted');

Markers and Lines

The marker parameter is used to specify the style of the markers, while the markersize parameter is used to adjust their size.

plt.plot([1,3],[7,10], c='r', marker='*', markersize=10);

# multiple points
plt.plot([1,3,5,7,9,11,13,13],[7,10,1,8,3,6,2,1], c='r', marker='*', markersize=20);

Pie Chart

plt.pie() is used to generate a pie chart. Here’s how the mentioned parameters work:

• The radius parameter adjusts the size of the pie chart.

• The autopct parameter is used to include and customize the display of percentage values.

  • ‘%.0f’: 0 reprecents the decimal place, ‘f’ represents float

expenses = ['housing', 'tuition', 'transportation', 'supplies', 'food']
cost = [700, 1000, 200, 100, 500 ]
color_set = ['y', 'r', 'g', 'orange', 'navy']

plt.pie(cost, colors = color_set, labels=expenses, radius=1, autopct='%.0f');

Barplot

plt.bar() is used to generate a bar plot.

plt.bar(expenses, cost);

# horizontal
plt.barh(expenses, cost, color='r' );

Boxplot

plt.boxplot() is used to generate a box plot, which represents the five-number summary:

1. Minimum

2. 1st quartile (median of the first half)

3. 2nd quartile (median)

4. 3rd quartile (median of the second half)

5. Maximum

• Open circles are used to represent outliers.

plt.boxplot([8,7,3,2,1,5,6,7,8,15]);

Histogram

plt.hist() is used to generate histograms, which represent the distribution of the data.

plt.hist([1,1,8,7,3,2,1,5,6,7,8,15,15,15,15]);

Save a Figure

• You can save a figure to a local computer or Google drive.

Local Computer

# save to a local computer
# same folder with your code
# name of the saveg picture is 'states_plot.png'

plt.scatter([2,4,5],[10,3,6])
plt.savefig('states_plot.png')

# save to a local computer
# to folder called data_files

plt.scatter([2,4,5],[10,3,6])
plt.savefig('data_files/states_plot.png')

Google Colab

# mount
# connection between colab notebook and drive
from google.colab import drive
drive.mount('/content/drive')

# save it to a folder in My Drive called data_files
# the name of the saved picture is states_plot.png

plt.scatter([2,4,5],[10,3,6])
plt.savefig('/content/drive/My Drive/data_files/states_plot.png')