rpch

How to specify pch by the value of a variable?

I'm making a plot of Y vs X for some discrete points in R. There is a third variable Z that has a value of either A or B, so I want to identify the third variable by pch in the plot. I can do the following.

plot(X, Y, pch=c(3,4)[Z])

However, I don't know whether Z=="A" is assigned to 3 or 4 in this case. How do I specify that Z=="A" is plotted as 4 and that Z=="B" is plotted as 3?

Thanks in advance.

Solution

  • You can subset from c(3, 4) based on value of Z like : 

    c(3,4)[(Z == "A") + 1]

    so when Z <- "A"

    Z <- "A"
c(3,4)[(Z == "A") + 1]
#[1] 4

    and when Z <- "B"

    Z <- "B"
c(3,4)[(Z == "A") + 1]
#[1] 3

    So the code would be 

    plot(X, Y, pch = c(3,4)[(Z == "A") + 1])

    Another option is to use ifelse

    plot(X, Y, pch = ifelse(Z == "A", 4, 3))