How to recode data frame columns depending on maximum values?

Question

I have a dataframe with dozens of columns and a few thousand rows. I would like to recode the numeric columns that have a maximum value of 8 in such a way that 8 becomes NA, and recode the numeric columns that have a maximum value of 9 in such a way that 8 becomes NA and 9 becomes 9999. For example,

mydf <- data.frame(a = c(1, 2, 8, 9), b = c(7, 8, 9, 10), c = c(4, 5, 6, 9), d = c(5, 6, 7, 8), e = c("a", "b", "c", "d"))

> mydf
  a  b c d e
1 1  7 4 5 a
2 2  8 5 6 b
3 8  9 6 7 c
4 9 10 9 8 d

would become:

> mydf
     a  b    c  d e
1    1  7    4  5 a
2    2  8    5  6 b
3   NA  9    6  7 c
4 9999 10 9999 NA d

I thought of doing this:

mydf1 <- mydf[,sapply(mydf, max) == 8]
mydf2 <- mydf[,sapply(mydf, max) == 9]
mydf1[mydf1 == 8] <- NA
mydf2[mydf2 == 8] <- NA
mydf2[mydf2 == 9] <- 9999

but I don't know how to bring the recoded variables from the new data frames back into the original data frame -- and I'm sure there are much more efficient solutions anyways.

Ronak Shah · Accepted Answer · 2020-09-06 03:02:46Z

1

You can check max value for each column using lapply and recode if it is either 8 or 9.

mydf[] <- lapply(mydf, function(x) {
  if(max(x) %in%  c(8, 9)) {
    x[x == 8] <- NA
    x[x == 9] <- 9999
  }
  x
})
mydf

#     a  b    c  d e
#1    1  7    4  5 a
#2    2  8    5  6 b
#3   NA  9    6  7 c
#4 9999 10 9999 NA d

answered Sep 6, 2020 at 3:02

Ronak Shah

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Comments

akrun · Accepted Answer · 2020-09-06 17:33:17Z

0

We can use tidyverse approaches to dynamically check if the column is numeric, then loop across those columns, check if 8 or 9 are %in% the max value, then use na_if to replace 8 to NA and replace to change the 9 to 9999

library(dplyr)
mydf %>%
    mutate(across(where(is.numeric), ~
   if(any(c(8, 9) %in% max(., na.rm = TRUE))) replace(na_if(., 8), .==9, 9999)))
#     a    c  d e
#1    1    4  5 a
#2    2    5  6 b
#3   NA    6  7 c
#4 9999 9999 NA d

edited Sep 6, 2020 at 17:33

answered Sep 6, 2020 at 17:25

akrun

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