The three most common open source technologies for writing data science programs are Python, SciLab, and R. Here's how to write program-defined functions in R.

Content: The R programming language is used for statistical data analysis and visualisation. R and the R Studio programming environment are a standard tool-set used worldwide for statistical analyses ...

But if you grasp the basics and want to learn data visualization fundamentals in R, I recommend Coursera’s guided project, Application of Data Analysis in Business with R Programming.