How to drop columns by name pattern in R?

Question

I have this dataframe:

state county city  region  mmatrix  X1 X2 X3    A1     A2     A3      B1     B2     B3      C1      C2      C3

  1      1     1            


        

Answer 1

Just as an additional answer, since I stumbled across this, when looking for the data.table solution to this problem.

library(data.table)
dt <- data.table(df)
drop.cols <- grep("1$", colnames(dt))
dt[, (drop.cols) := NULL]