If you spend time with R regularly then you should have the basics of data manipulation & plotting down within a couple of weeks. The more esoteric functions will take time to master. These are PDF cheat sheets that can be printed out. Keep them handy as you work with R.
R Coding Cheat Sheet 2020
help.start() - This first link doesn't actually take you to another site because it isn't a resource on the web, it's contained with R. To access it just type help.start() at the prompt and a collection of manuals will appear in your browser window. Pretty handy reference tool, eh?
Lattice R Graphics Cheat Sheet David Gerard 2019-01-22 Abstract: IreproducesomeoftheplotsfromRstudio’sggplot2cheatsheetusingjustthelatticeRpackage. 280k members in the coding community. ??♂️ Why to support CMS-agnosticism, the GraphQL API for WordPress was split to 90 packages, and benefits and drawbacks of this approach.
R Reference Card - This is the most popular reference card. This same document is available from a number of sites and includes info on input & output, getting help, working with variables & arrays, plotting & more. You want this one.
R Coding Cheat Sheet
R for Data Mining - This document was written by RDataMining.com. It includes info on classification, clustering, social network analysis, big data and more. This is very handy if you're interested in knowledge discovery & data mining.
R Lists Cheat Sheet
R Style Guide - This resource is more than a cheat sheet. Google's internal R user community put together this guide for clean R code that covers syntax & conventions that are unique to R. I include it here because I've refered to it quite a bit in my own work. Your code will be easy to read & maintain if you follow these guidelines.