I'm working with a data frame where the color of an object (red or green) was recorded in ordinal classes corresponding to percent coverage.

I am looking to replace all the classes with their corresponding numerical value, which are stored in a second data frame. What is the most efficient way to go about that?

Example data:

df1 <- data.frame(
    object = c("A", "B", "C"),
    red = c(1, 0 ,2),
    green = c(3, 4, 2)
)

df2 <- data.frame(
    ordinal = c(0, 1, 2, 3, 4),
    percent = c(0, 25, 50, 75, 100)
)

> print(df1)
  object red green
1      A   1     3
2      B   0     4
3      C   2     2

> print(df2)
  ordinal percent
1       0       0
2       1      25
3       2      50
4       3      75
5       4     100

Desired outcome:

  object  red  green
1      A   25     75
2      B    0    100
3      C   50     50

My dataset is too large to do this manually, and the actual ordinal classes are not evenly spaced, so I can't just use math to get the numbers.

I have tried using case_when(), but I keep getting an error:

df1 <- df1 %>% 
+   case_when(df1[,2:3] == df2$class, df2$percent)

Error in `case_when()`:
! Case 1 (`.`) must be a two-sided formula, not a  object.

For what it's worth, I am still relatively new to R.