r-具有多个列的ifelse（应用）

Question

I am new to understanding the apply world and while i am starting to understand the concept, have trouble with the application.

i have multiple columns with "Y" in as a value that I would like to change to the last letter of the column name.

I would like to use the following to get a the list of columns to apply the function to:

flaggs2015 <- grep("Flag", names(ItemStats_2015))

here is an example of what i would like to do with 1 column:

ItemStats_2015$Item_Flag_A <- ifelse(ItemStats_2015$Item_Flag_A == "Y", str_sub(flaggs2015[1], -1, -1), NA)

except i would, obviously, like to do it over any column with 'Flag' in the name at the same time.

Here is sample data:

Item_ID Item_Flag_A     dummy column    Item_Flag_B     Item_Flag_C
54434   Y               red                         
85068                   green                           
85070   Y               purple                          Y       
85072                   orange                          
85074   Y               red                         
85078   Y               green                           
85080   Y               purple          Y           
85086                   orange                          
85088                   red                         

Answer 1

Im stuck with that:

df <- data.frame(Item_ID = 1:3, Item_Flag_A = c("", "Y", ""), Dummy = 1:3, Item_Flag_B = c("Y", "", ""))
idx <- grep("Flag", names(df), value = T)

sapply(idx,  function(x) {
  df[, x] <<- ifelse(df[, x] == "Y", str_sub(x, -1, -1), NA)
})