Example of using plyr::mapvalues

mapvalues.R

library(plyr)
library(dplyr)

# Create a vector of numbers

num_vec <- round(runif(n = 100, min = 1, max = 26))

# Convert these to letters using the inbuilt letters vector

letter_vec <- letters[num_vec]

# Print to check

num_vec
letter_vec

# Create a data.frame

df <- data_frame(
  letter_column = letter_vec 
  )

df

# Now map the values back to numbers using the inbuilt letters vector

df %>%
  mutate(
    numbers = mapvalues(
      letter_column,
      from = letters,
      to = 1:26
      )
    )