Recode column of character variables in one data frame with numeric values in another data frame

Question

I have the following dataframes:

df <- data.frame(x=c('a', 'b', 'c'), y=c(.1,.2,.3))
xev_values <- data.frame(a=.01, b=.02, c=.03)

How do I recode the character variables in the x column of df with the numeric values in xev_values so that I have a new dataframe?

new_df <- data.frame(xev=c(.01,.02,.03), y=c(.1,.2,.3))

I see how to do this "manually" with recode:

new_df <- data.frame(xev=recode(df$x, 'a'=.01, 'b'=.02, 'c'=.03), y=df$y)

Answer 1

We can convert xev_values to long-format, conduct a join, and then select the columns.

library(tidyverse)

df2 <- df %>%
  left_join(xev_values %>% gather(x, xev), by = "x") %>%
  select(xev, y)
df2
#    xev   y
# 1 0.01 0.1
# 2 0.02 0.2
# 3 0.03 0.3