More Visualization CT @ VT Why Functions How can code be made - - PowerPoint PPT Presentation

Introduction to Computational Thinking

More Visualization

CT@VT Why Functions

 How can code be made available for others to

use?

 Cut/paste of code (as we did for Blockly Python)

works only for small amounts of code

 Need better ways to organize and reuse large

amounts of code

 Python provides three ways

 Function – code that performs a single action



Simple action: round a number



Complex action: generate a visualization

 Module – a collection of related functions



e.g., all of visualization functions

 Package – a collection of related modules



e.g., all of the modules that do different forms of visualization

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CT@VT Packages and Modules



Matplotlib: commonly used in Python to create visualizations (see http://matplotlib.org/gallery.html).



Syntax: matplotlib.pyplot.show()



Shorthand: import matplotlib.pyplot as plt ... plt.show()

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package module matplotlib pyplot plot show functions

CT@VT Functions in 3 easy steps

 Step 1: functions have names

 show() # show the visualization

 Step 2: functions may have parameters

 plot(data) # plot the list data

 Step 3: functions may return a value

 val = sqrt(number) # square root

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Notes



The user documentation tells you what a function does and what you need to use it



You do not need to know how a function is implemented to use it (and you often don’t care)



Reusing functions is a highly valued professional practice

CT@VT Three simple visualizations Name Function Name Typical Usage Line plot plot(x) Change or variation (sometimes

• ver time)

Scatter plot scatter(x,y) Relation between x and y Histogram (aka Bar Chart) hist(x) Distribution over categories of x

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Simple statistical measures: mean (average) range (min-max) median (middle value) More complex statistical measures: regressions …..

CT@VT Line plot visualizations

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import earthquakes # get all the reports of earthquakes of the current day quakes = earthquakes.get_report('day', 'all') quake_list = quakes[“earthquakes”] #create an empty list significance_list = [] for quake in quakes_list: # add the significance of the next earthquake to the list significance_list.append(quake["significance"]) plt.plot(significance_list) plt.show()

Click to save

Question: What is the variation in earthquake intensity?

CT@VT Scatter plot visualization

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Question: What is the relationship between the depth and magnitude of earthquakes?

import earthquakes import matplotlib.pyplot as plt … depths = [ … ] magnitudes = […] … plt.scatter(depths, magnitudes) plt.show()

CT@VT Histogram visualization

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Question: What is the distribution of the magnitudes of earthquakes? import earthquakes import matplotlib.pyplot as plt … magnitudes = [ … ] … plt.hist(magnitudes) plt.show()

CT@VT Next Steps

 Work as usual to complete the classwork

for today

 Homework gives you more practice with

these ideas

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