[SOLVED] Taking column means as part of a function

Issue

I have the following function:

estimate = function(df, y_true) {
        
        R = nrow(df)
        
        y_estimated = apply(df, 2, mean)
        
        ((sqrt( (y_estimated - y_true)^2 / R)) / y_true) * 100
}


df = iris[1:10,2:4]
y_true = c(3, 1, 0.4)
estimate(df = df, y_true = y_true)

user:bird provided this and works great, however, I also need to find the means by group. So if we change the df to df= iris[,2:5], how to do I find the means of each column by Species to use in the function. I figured something like this would work- but not luck:

estimate = function(df, y_true, group) {
  
  R = nrow(df)
  
  y_estimated = df %>% group_by(group) %>% apply(df, 2, mean)
  
  ((sqrt( (y_estimated - y_true)^2 / R)) / y_true) * 100
}



df = iris[2:5]
y_true = c(3, 1, 0.4)
group=df$Species 

estimate(df = df, y_true = y_true, group=group)

Using colMeans also did not work.

This is an extension of this post which explains the purpose of each variable.

Solution

Rather than modifying your function, you can keep the function as-is and apply it group-wise to your data. If you use group_by and then group_modify, the input to the function you pass to group_modify is the data frame, subset to the rows in that specific group.

estimate = function(df, y_true) {
        
        R = nrow(df)
        
        y_estimated = apply(df, 2, mean)
        
        ((sqrt( (y_estimated - y_true)^2 / R)) / y_true) * 100
}


df = iris[2:5]
y_true = c(3, 1, 0.4)

library(dplyr, warn.conflicts = FALSE)

df %>% 
  group_by(Species) %>% 
  group_modify(~ as.data.frame.list(estimate(., y_true)))
#> # A tibble: 3 × 4
#> # Groups:   Species [3]
#>   Species    Sepal.Width Petal.Length Petal.Width
#>   <fct>            <dbl>        <dbl>       <dbl>
#> 1 setosa           2.02          6.53        5.44
#> 2 versicolor       1.08         46.1        32.7 
#> 3 virginica        0.123        64.4        57.5

^{Created on 2022-02-24 by the reprex package (v2.0.1)}

Answered By – IceCreamToucan

Answer Checked By – Mary Flores (BugsFixing Volunteer)