Finding the location of half the max value in a column

Question

I have a list of data frames, and I'd like to apply a function to that list to find the location in the "julian" column that corresponds to half the max value in the "total_cover" column. Here's some data that represents the data I have:

df1 <- data.frame(julian = c(81,85,88,97,101,104,126,167),
                  total_cover = c(43,52,75,92,94,97,188,172))
df2 <- data.frame(julian = c(81,85,88,97,101,104,126,167),
                  total_cover = c(30,55,73,80,75,85,138,154))
df3 <- data.frame(julian = c(107,111,115,119,123,129,131,133,135,137),
                  total_cover = c(36,41,43,47,55,55,55,65,75,80))

data.list <- list(df1=df1,df2=df2,df3=df3)

The code below is what I've tried, but I'm not getting the correct output. This doesn't seem to be finding the julian day that corresponds to half the max value

unlist(lapply(X = data.list, FUN = function(x){
        x[which.max(x[["total_cover"]] >= which.max(x[["total_cover"]])/2), "julian"]
}))

output:
df1  df2  df3
81   81   107

My ideal output would be what's shown below, with the julian dates that correspond to >= max(total_cover)/2

df1  df2  df3
101  97   111

Using R 4.2.2

Answer 1

I believe the following answers the question.

sapply(data.list, \(x) {
  half_max <- max(x$total_cover)/2
  d <- abs(x$total_cover - half_max)
  is.na(d) <- x$total_cover < half_max
  x$julian[which.min(d)]
})
#> df1 df2 df3 
#> 101  97 111

^{Created on 2022-12-13 with reprex v2.0.2}