KableExtra conditionally formatting specific rows on a column

Question

I have just learnt KableExtra and know to how to use conditionally formating the entire column using mutate() as explained in the doc using mutate such as:

mutate(
   mpg = cell_spec(mpg, background = ifelse(mpg > 20, "red", "blue"))
)

But what I don't know is, how to change background colours of only certain rows in each column whilst all rows are being displayed.

For example, my data:

df <- data.frame( region1 = c("A", sample(1:5,3)),
                  region2 = c("B", sample(1:5,3)),
                  region3 = c("C", sample(1:5,3)),
                  region4 = c("A", sample(1:5,3)) )

Now I want to format only second and third row. I dont want to change the color background of first and last row. These second and third row should be 'red' when above 1, or yellow when equal to 1 or green when below 1.

Some one could help me this?

Answer 1

Here's an example that ignores the first and last rows and colours according to value, like you say, but ignores letters.

First, I load the libraries.

# Load libraries
library(knitr)
library(kableExtra)

Next, I create a dummy data frame.

# Create data frame   
df <- data.frame( region1 = c(sample(c(-5:5, letters[1:5]), 10, replace = TRUE)),
                  region2 = c(sample(c(-5:5, letters[1:5]), 10, replace = TRUE)),
                  region3 = c(sample(c(-5:5, letters[1:5]), 10, replace = TRUE)),
                  region4 = c(sample(c(-5:5, letters[1:5]), 10, replace = TRUE)), stringsAsFactors = FALSE )

Here, I define the function for formatting cells. I ignore the first and last rows and check if the character is a letter or number, then colour accordingly.

foo <- function(x, n, nmax){
  cell_spec(x, background = ifelse(is.na(as.numeric(x)), "white",
                                   ifelse(n == nmax | n == 1, "white",
                                          ifelse(x > 1, "red",
                                                 ifelse(x < 1, "green", "yellow")))))
}

Finally, I apply the function.

df %>% 
  mutate_all(funs(foo(., n = row_number(), nmax = n()))) %>% 
  kable(escape = FALSE) %>% 
  kable_styling()

Answer 2

That's not a good design for a dataframe: columns need to be all one type, so your numbers will be coerced to character.

Nevertheless, you can do what you ask for as follows.

fixcol <- function(col) {
  x <- as.numeric(col[2:3])
  x <- cell_spec(x, background = ifelse(x > 1, "red", ifelse(x == 1, "yellow", "green")))
  col[2:3] <- x
  col
}

df <- as.data.frame(lapply(df, fixcol))
kable(df, escape = FALSE)