Making custom functions in R involving summation - r

Question

I am a novice in R asked to compute for a descriptive statistic called dominance (D; expressed as a percentage). D is basically defined as the mean abundance (MA) value of x divided by the sum of MA values of x to i. MA meanwhile is defined as the sum of all values in a vector over the length of the said vector. Here is how I normally approach things:
#Example data
x <- c(1, 2, 3)
y <- c(4, 5, 6)
z <- c(7, 8, 9)
#Mean abundance function
mean.abundance <- function(x){
N_sum <- sum(x)
N_count <- length(x)
N_sum/N_count
}
#Percent dominance function (workaround)
percent.dominance <- function(x, ...){
MA_a <- (x)
sum_MA_i <- sum(x, ...)
(MA_a/sum_MA_i)*100
}
MA_x <- mean.abundance(x)
MA_y <- mean.abundance(y)
MA_z <- mean.abundance(z)
MA <- c(MA_x, MA_y, MA_z)
MA
D_x <- percent.dominance(MA_x, MA_y, MA_z)
D_y <- percent.dominance(MA_y, MA_x, MA_z)
D_z <- percent.dominance(MA_z, MA_x, MA_y)
D <- c(D_x, D_y, D_z)
D
That approach alone already gives me the %D values I am looking for. My problem is that my (perfectionist) PI is asking me to compute for the %D values directly using vectors x, y, and z (and not stepwise by means of calculating MA values then using vectors MA_x, MA_y, and MA_z to calculate for %D). I am stumped making a custom function for %D that involves vectors containing raw data; here is a failed attempt to revise said custom function, just to give a general idea.
#Percent dominance function (incorrect)
percent.dominance <- function(x, ...){
MA_a <- sum(x)/length(x)
sum_MA_i <- sum(x, ...)/length(x, ...)
(MA_a/sum_MA_i)*100
}

Answer 1

You can capture the optional data passed with list(...) and make the following changes to the function -
percent.dominance <- function(x, ...){
data <- list(...)
MA_a <- sum(x)/length(x)
sum_MA_i <- sum(x, unlist(data))/(length(data) + 1)
(MA_a/sum_MA_i)*100
}
percent.dominance(x, y, z)
#[1] 13.33333
percent.dominance(y, x, z)
#[1] 33.33333
percent.dominance(z, x, y)
#[1] 53.33333