Circular assignment in R

Question

I found a line the the genetics package that goes like this:

P <- D <- Dprime <- nobs <- chisq <- p.value <- corr <- R.2 <- P

note P is both at the beginning and at the end. What does it mean?

Answer 1

This construct will assign the value of P to variables with each of the other names given in the string of <-s. That assignment will take place in the current environment.

Thus, if the variable named P on the far right is not in the current environment, a new variable P will be created in the current environment.

To see this in action, run the following from a fresh R session:

ls()
# character(0)
mean <- a <- b <- mean
ls()
# [1] "a"    "b"    "mean"