R Cheat Sheets by Mark the Graph.
Basic
Brief Introduction to Language Elements and Control Structures
Data Frames
Basic List of Useful Functions
tRips and tRaps for new players
Vectors and Lists
Intermediate
Avoiding For-Loops
Factors
OOP and S3 Classes
Writing Functions
Advanced
Environments, Frames and the Call Stack
R5 Reference Classes
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Which may be one of the primary reasons for taking the time and effort to create them.
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