rmaxmatchcorrespondence

Find value corresponding to maximum in other column


I have a data frame similar to as follows:

x <- c(1, 2, 3, 4, 5)
y <- c(1, 2, 3, 2, 1)
df <- data.frame(x, y)

I want to find the value of x when y is at its maximum. I know that I can find the max of y with this:

max(df$y)

But I don't know how to match it, and I think there's probably a better way.


Solution

  • Using dplyr:

    # install.packages(dplyr)
    library(dplyr)
    
    df %>% 
        filter(x == max(y)) %>% # filter the data.frame to keep row where x is maximum
        select(x) # select column y
    

    Alternatively to return a vector

    df %>% 
        filter(x == max(y)) %>% 
        pull(x) # pull the variable y
    

    using base R:

    df[df$x == max(df$y), "x"]