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Lecture 2 – Chart with Matplotlib

Information Literacy II – EN(IL2) Course

Today's schedule

Review of last week

Overview of other toolsMicrosoft Excel

Google Sheets

Introduction to Python (cont'd)

Other type of graphs

Last week review (and more)

Saving chart to file

Use plt.savefig(filename)

File type is decided by extension:figure.pdf or figure.png or figure.jpg or …

Mini-exercise:Save the same plot using .pdf and .pngDo you see any difference?What are the advantages/drawbacks of these formats?

Comparing .pdf or .png

Both are portable: readable on (almost) all computersPdf files can contain vector graphicsPng files contain only raster graphics

Possible to zoom with pdf files, but potentially larger files for complex plot (e.g. with many points)Both formats can be used in LaTeX

Other tools (no slides – only demo)

Introduction to Python

Python (again)List ComprehensionsCreate new lists easilyCan be used to modify data

Simple examplesnumbers = [1, 2, 3, 4, 5, 6, 7]squared = [x**2 for x in numbers]total = sum(numbers)percentage = [x/total*100 for x in numbers]

Mini-exercise:Given a list of numbers, create- a list containing the last digit of each elements- a list containing the first digit of each elements

Remark: the second question is HARD; please try but I do not expect you to be able to do it without help.

# InputL = [104, 71, 234, 78, 9, 23]

# Outputlast = [4, 1, 4, 8, 9, 3]first = [1, 7, 2, 7, 9, 2]

Other type of charts

Charts typeMany types of charts:Line Chart

Bar Chart

Histogram

Pie Chart

Gantt Chart

Need to know when/how to use each of them

All images from Wikipedia.

foreignBStudents = [173, 172, 194, 248, 276,294, 307, 282, 267, 252,238, 220, 187, 170, 174,186, 210, 239, 249, 267]

years = list(range(2000, 2020))

# Axis labels and graph titleplt.xlabel("Academic year")plt.ylabel("Number of students")plt.title("Number of undegraduate foreign students in Titech")

# Small modifications of axisplt.xticks([2000, 2005, 2010, 2015, 2019])plt.ylim(0, 320)

# Only this line change compared to before!plt.bar(years, foreignBStudents)

# Save the generated graph to fileplt.savefig("BStudentsTokyTech.png")

Bar Chart

Pie ChartExercise (difficult):

- Google “statistics tokyo tech” or find on Tokyo Tech website

- Look for information on how to draw pie charts

- Draw a graph similar to the one on the right

(It may be difficult to display the percentage values)

plt.pie() creates the pie chart

It takes the sizes of each slice and the labels

Find how to add the percentage values by yourself

Look for examples online. Impossible to guess.

Use plt.axis(‘equal’) to have a circular pie

Try without this line and see the result

names = ['Science', 'Engineering', 'Materials', 'Computing', 'Life', 'Environment']sizes = [151, 358, 183, 92, 150, 134]

plt.pie(sizes, labels=names)plt.axis('equal')

plt.title('Admission quota (AY2016)')plt.savefig("quota.png")

Pie Chart