R programming is not a difficult programming language to learn. You can learn the syntactic structure of R in just one or two days. Since R is majorly used for statistical analysis, you need to focus on learning statistics as well. It will help you understand the graphical visualizations plotted using R. To become an expert in R programming, you must start implementing the techniques of R on various types of datasets to understand how to visualize data.
If you are looking for an online course to learn R programming, check out this R Programming Online Course by Intellipaat.