R - Vary by Row the Rounding of Digits Produced by knitr::kable

Question

I am trying to produce a markdown table using knitr::kable where the rounding of digits varies by rows. For example, suppose I have the following data.frame:

exa         


        

Answer 1

If you have more than 4 or 5 rows, it may be worth using mapply() to avoid having to repeat formatC(...) once for each row.

example.df <- data.frame(a = c(0.1234, 2000), b = c(0.5678, 3000))

example.df1 <- data.frame(t(example.df))  # Transpose for easy iteration
example.df1 <- mapply(  # Iterate over each column
  function(df, digits) {
    formatC(df, format="f", digits=digits)
  },
  df=example.df1, digits=c(2, 0)
)
example.df1 <- data.frame(t(example.df1))  # Transpose back
names(example.df1) <- names(example.df)  # Re-create names
kable(example.df1, row.names=FALSE)

In the above code, you simply need to set df= to the data.frame or matrix you want to turn into a table and digits= to a vector indicating how many digits you want in each row.

Such a method could also be turned into a function if you were repeating it over multiple tables.

digitsByRows <- function(df, digits) {
  tmp0 <- data.frame(t(df))
  tmp1 <- mapply(
    function(df0, digits0) {
      formatC(df0, format="f", digits=digits0)
    },
    df0=tmp0, digits0=digits
  )
  tmp1 <- data.frame(t(tmp1))
  names(tmp1) <- names(df)
  return(tmp1)
}
kable(digitsByRows(example.df, c(2, 0)), row.names=FALSE)

Answer 2

As pointed out by @user20650, one solution consists in converting the format of the entries in your dataframe in R before passing the data to knitr. It could be done like this:

example.df <- rbind(formatC(as.numeric(example.df[1,]),format="f",digits=2),
                    formatC(as.numeric(example.df[2,]),format="d"))
colnames(example.df) <- c("a","b")

This gives the following output:

> kable(example.df, align="r")

|    a|    b|
|----:|----:|
| 0.12| 0.57|
| 2000| 3000|