Instead of traditional pie charts that rely on angles and arc lengths to show parts of a whole, try this easiertoread version.
R

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How to Make Square Pie Charts in R

R in the data journalism workflow at FiveThirtyEight
R has found its way into a good number of news groups who…

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Annotating Charts in R
Let the data speak for itself they say. That doesn’t work a lot of the time, and when that happens, you need to explain.

5 Tips for Learning to Code for Visualization
Here are some tips to get you started, based on my own experiences with R, and more recently, the JavaScript library d3.js.

A Course for Visualizing Time Series Data in R
Learn to visualize temporal patterns in a couple of days.

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Drawing Lines and Segments in R
Show connections and changes over time with start and end points.

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Drawing Circles and Ellipses in R
Whether you use circles as visual encodings or as a way to highlight areas of a plot, there are functions at your disposal.

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Drawing Squares and Rectangles in R
R makes it easy to add squares and rectangles to your plots, but it gets a little tricky when you have a bunch to draw at once. The key is to break it down to the elements.

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Voronoi Diagram and Delaunay Triangulation in R
The
deldir
package by Rolf Turner makes the calculations and plotting straightforward, with a few lines of code. 
Comparing ggplot2 and R Base Graphics
Figure out which is best with a sidebyside comparison.

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Adding Legends in R
Make sure you explain your visual encodings so that others can interpret them.

Emergency room data in R
For my graphic on emergency room visits over time and the other on…

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How to Customize Axes in R
For presentation purposes, it can be useful to adjust the style of your axes and reference lines for readability. It’s all about the details.

R growth on StackOverflow reigns supreme
Joshua Kunst did a quick analysis on tag usage on StackOverflow, the question…

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How to Make an Animated Pyramid Chart in R
Make a bunch of charts, string them together like a flip book, and there’s your animation. Sometimes good for showing changes over time. Always fun to play with.

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How to Make Bivariate Area Charts in R
Quickly compare two time series variables with this linearea chart hybrid that originated in the 1700s. Also known as: difference chart.

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How to Make Maps in R That Include Alaska and Hawaii
The conterminous United States always gets the attention, while Alaska and Hawaii are often left out. It is time to bring them back into view.

Tufte style charts in R
Lukasz Piwek is chipping away at a collection of Tuftestyle charts using R,…

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How to Map and Use GeoTIFF Files in R
It’s like working with a bunch of tiny dots, and oh look, all of sudden patterns emerge.

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How to Make Horizon Graphs in R
The relatively new and lesser known time series visualization can be useful if you know what you’re looking at, and they take up a lot less space.