Math   [+++++---]  
R      [++++----]
Python [++------]
Excel  [+++++---]
VBA    [++------]
SQL    [+++-----]

Books to read

• R For Data Science
• Advanced R + Advanced R Solutions

Useful links

• Tidyverse Style Guide
• Programming with dplyr
• How do I make a list of data frames?
• Top 50 ggplot2 Visualizations
• Design of Experiments (DoE) & Analysis of Experimental Data
• What does .SD stand for in data.table in R