Pie Charts

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From the course by IBM

Data Visualization with Python

46 оценки

IBM

Data Visualization with Python

46 оценки

Course 2 of 4 in the Specialization Applied Data Science

"A picture is worth a thousand words". We are all familiar with this expression. It especially applies when trying to explain the insight obtained from the analysis of increasingly large datasets. Data visualization plays an essential role in the representation of both small and large-scale data. One of the key skills of a data scientist is the ability to tell a compelling story, visualizing data and findings in an approachable and stimulating way. Learning how to leverage a software tool to visualize data will also enable you to extract information, better understand the data, and make more effective decisions. The main goal of this Data Visualization with Python course is to teach you how to take data that at first glance has little meaning and present that data in a form that makes sense to people. Various techniques have been developed for presenting data visually but in this course, we will be using several data visualization libraries in Python, namely Matplotlib, Seaborn, and Folium.

From the lesson

Basic and Specialized Visualization Tools

In this module, you learn about area plots and how to create them with Matplotlib, histograms and how to create them with Matplotlib, bar charts, and how to create them with Matplotlib, pie charts, and how to create them with Matplotlib, box plots and how to create them with Matplotlib, and scatter plots and bubble plots and how to create them with Matplotlib.

Scatter Plots4:17

Meet the Instructors

Alex Aklson
Ph.D., Data Scientist
IBM Cognitive Class

In this video, we will learn about another visualization tool: the pie chart,

and we will learn how to create it using Matplotlib.

So what is a pie chart? A pie chart is a circular statistical graphic divided

into slices to illustrate numerical proportion. For example, here is a pie

chart of the Canadian federal election back in 2015 were the Liberals in red

won more than 50% of the seats in the House of Commons. That is why the red

color occupies more than half of the circle. So how do we create a pie chart

with Matplotlib? Before we go over the code to do that, let's do a quick recap

of our dataset. Recall that each row represents a country and contains

metadata about the country such as where it is located geographically and whether

it is developing or developed. Each row also contains numerical figures of

annual immigration from that country to Canada from 1980 to 2013.

Now let's process the dataframe so that the country name becomes the index of

each row. This should make retrieving rows pertaining to specific countries a

lot easier. Also let's add an extra column which represents the cumulative

sum of annual immigration from each country from 1980 to 2013. So for

Afghanistan for example, it is 58,639, total, and for Albania, it is

15,699 and so on. And let's name our dataframe df_canada. So now

that we know how our data is stored in the dataframe df_canada, say

we're interested in visualizing a breakdown of immigration to Canada

continent wise. The first step is to group our data by

continent using the continent column and we use pandas for this. We call the

pandas groupby function on df_canada and we sum the number

of immigrants from the countries that belong to the

same continent. Here is the resulting dataframe, and let's name it

df_continents. The resulting dataframe has six rows, each

representing a continent and 35 columns representing the years from 1980 to 2013

plus the cumulative sum of immigration for each continent. And now we're ready

to start creating our pie chart. We start with the usual, importing Matplotlib as

mpl and its scripting layer the pyplot interface as plt. Then we call the

plot function on column total of the dataframe df_continents and

we set kind equals pie to generate a pie chart. Then to complete the figure we

give it a title. Finally we call the show function to

display the figure. And there you have it. A pie chart that depicts each continent's

proportion of immigration to Canada from 1980 to 2013. In the lab session, we will

go through the process of creating a very professional-looking and

aesthetically pleasing pie chart and transform the pie chart that we just

created into one that looks like this. So make sure to complete this module's lab

session. One last comment on pie charts. There are some very vocal opponents to

the use of pie charts under any circumstances. Most argue that pie charts

fail to accurately display data with any consistency. Bar charts are much

better when it comes to representing the data in a consistent way and getting the

message across. If you're interested in learning more about the arguments

against pie charts, here is a link to a very interesting article that discusses

very clearly the flaws of pie charts. You can also find the link under the video.

And with this we conclude our video on pie charts. I'll see you in the next

video.

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