Python-3.4.3/C2/Plotting-Charts/English

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Title of script: Plotting Charts

Author: Trupti Kini, Thirumalesh H S

Keywords: Python, IPython, pylab, scatter plot, charts, matplotlib help


Visual Cue Narration
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Hello friends. Welcome to the tutorial on plotting charts
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Learning Objectives

At the end of this tutorial, you will be able to -
  • Create pie charts
  • Create bar charts and
  • Find more information on matplotlib
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System Specifications

To record this tutorial, I am using
  • Ubuntu Linux 14.04 operating system
  • Python 3.4.3
  • IPython 5.1.0
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Pre-requisites

To practice this tutorial, you should know how to
  • run basic Python commands on the ipython console
  • Load data from files and
  • Plot data.

If not, see the relevant Python tutorials on this website.

Open [Terminal] and type

ipython3


Let us first open the Terminal by pressing Ctrl+Alt+T keys simultaneously.

Now, type ipython3 and press Enter.

[IPython console]

type %pylab and press Enter.

Let us initialize the pylab package.

Type %pylab and press Enter.

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Pie chart

A pie chart is a circular chart divided into sectors, to illustrate numerical proportion
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pie() function

Syntax:

pie(values, labels= labels)

  • values – the data to be plotted
  • labels – the label for each wedge in the pie chart


The syntax for pie() function is as follows:

pie inside parentheses values comma labels equal to labels

  • where values are the data to be plotted
  • and labels – the label for each wedge in the pie chart
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Exercise 1

  • Plot a pie chart representing the profit percentage of company A.
  • Use the data from file company-a-data.txt available in the code file link of this tutorial
[File browser]

Open the file company-a-data.txt and show the content

The data file has two columns with a set of values in each column.

The first column represents years. The second column represents the profit percentages.

[IPython Terminal]

year, profit = loadtxt('company-a-data.txt', unpack = True)

To produce a scatter plot, we first need to load the data from the file using loadtxt command.

Let us clear the terminal.

Type

year comma profit equal to loadtxt inside parentheses inside single quotes add the path of the file company-a-data.txt comma unpack equal to True and press Enter

unpack equal to True --> returns the transposed array of data.

[Ipython Terminal]

clf()

pie(profit,labels=year)

Type clf open and close parentheses to clear the plot window, if any plots executed previously.

Type pie(profit comma labels equal to year) and press Enter.

[Plot Window]


Show pie chart plot

Notice that we passed two arguments to the function pie().

First one being the values, which is profit in our case.

The next one being the set of labels to be used in the pie chart, which is year in our case.

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Exercise 2

Pause the video here.

Try out the following exercise and resume the video.


Plot a pie chart with the same data with the following colors for each wedges.

  • white, red, black, magenta,
  • yellow, blue, green, cyan,
  • yellow, magenta and blue.

Hint: In your ipython interpreter, try typing pie question mark.

[IPython Terminal]

clf()

pie(profit,labels=year,colors=('w','r','k','m','y','b','g','c','y','m','b'))

Solution to Exercise 2

Clear the plot window by typing clf open and close parentheses and press Enter.

Type pie inside parentheses profit comma labels equal to year comma colors equal to inside parentheses the color codes and press Enter.

This will display a pie chart with each wedge having the color as specified in the parameters.

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Bar chart

A bar chart is a chart
  • with rectangular bars
  • with lengths proportional to the values that they represent.
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bar() function

The syntax for bar chart is:

bar inside parentheses x comma y

  • where x – a sequence of data and
  • y - a sequence of data, the same length of x
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Exercise 3

  • Plot a bar chart representing the profit percentage of company A.
  • Use the data from file company-a-data.txt.
[IPython Terminal]


clf()

bar(year, profit)

Solution to Exercise 3

Clear the plot window by typing clf open and close parentheses

Type bar open and close parentheses year comma profit and press Enter.

This will display a bar chart representing the profit percentage of company A

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Exercise 4

Plot a bar chart as shown in the image:

Hint: Bar chart is not filled and which is hatched with 45o slanting lines.

The data for the chart may be obtained from the file company-a-data.txt.

Hint: In your ipython interpreter, try typing bar question mark


[Ipython Terminal]

clf()

bar(year,profit,fill=False,hatch='/')

Solution to Exercise 4

Clear the plot window by typing clf open and close parentheses

Type bar open and close parentheses year comma profit comma fill equal to False comma hatch equal to inside single quotes slanting line and press Enter.

This will display a bar chart which is not filled and which is hatched with 45o slanting lines

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"Getting help on matplotlib"

{SHOW WEBSITE while narrating}

matplotlib.sourceforge.net/users/screenshots.html

and also at matplotlib.sourceforge.net/gallery.html

Help about matplotlib can be obtained from matplotlib.sourceforge.net/contents.html

More plots can be seen at the following links

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Summary slide

This brings us to the end of this tutorial.

In this tutorial we learnt to,

  • Plot a pie chart using pie() function
  • Plot a bar chart using bar() function
  • Access the matplotlib online help
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Assignment

  • bar(x, y, color='w', hatch='/')
  • bar(x, y, fill=False, hatch='//')
  • bar(x, y, fill=False, hatch='|')
  • bar(x, y, color='w', hatch='\')
Here are some self assessment questions for you to solve.

1.What statement can be issued to generate a bar chart with vertical line hatching?


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Solution to assignment

And the answer is,


  1. bar x comma y comma fill equal to False comma hatch is equal to a vertical line) is the correct option to generate a bar chart with vertical line hatching.


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Forum

Please post your timed queries in this forum.
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Fossee Forum

Please post your general queries on Python in this forum.
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Textbook Companion

FOSSEE team coordinates the TBC project.
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Acknowledgment

http://spoken-tutorial.org

Spoken Tutorial Project is funded by NMEICT, MHRD, Govt. of India.

For more details, visit this website.

Previous slide This is Trupti Kini from FOSSEE IIT Bombay signing off.

Thank you.

Contributors and Content Editors

Nancyvarkey, Nirmala Venkat, Trupti