How to compute the conditional probability in R?

Question

Let's suppose I have these two vectors:

x = rnorm(20)
y = rnorm(20)

I want to compute the probability that y > 0 given that x > 0 . In other words, I want the frequency that my y > 0 when x > 0 . Can anyone show me how to code this in R?

Answer 1

To make the results reproducible, I will use set.seed

set.seed(42)
x = rnorm(20)
y = rnorm(20)

You can just subset the data to select the ones where x>0 and then count what proportion of those have y>0

PosX = which(x>0)
sum(y[PosX] > 0)/length(PosX)
[1] 0.6