基于其他列 R 的因素重命名级别

Question

I have a large dataframe where names (col1) should be nested within location name (col2). In the example below "d" from col1 should be within "z" of col2 but is listed as "y" in the eighth element. I cannot just rename "y" in col2 as it is correct in most places. I need to rename "y" to "z" only when col1 == "d". It is a large dataframe with multiple example so it is also not possible just to rename the element

col1<-c("a","b","c","d","a","b","c","d")
col2<-c("x","y","z","z","x","y","z","y")
df<-data.frame(col1,col2)

Answer 1

This would be easy if you can create a data frame lookup with the correct combination of col1 and col2 . You can then just left_join your original data frame with the lookup .

library(dplyr)

# Create a lookup table. In reality you probably need to create this with other methods.
lookup <- df %>%
  distinct() %>%
  filter(!(col1 %in% "d" & col2 %in% "y"))

# join col1 to the lookup
df2 <- df %>%
  select(-col2) %>%
  left_join(lookup, by = "col1")
df2
#   col1 col2
# 1    a    x
# 2    b    y
# 3    c    z
# 4    d    z
# 5    a    x
# 6    b    y
# 7    c    z
# 8    d    z