if I want to specify y-coordinates for the heights of horizontal lines to go across a plot.
 
x <- c(1,2,3,6,4,8,4,7)
y <- c(3,2,7,4,5,4,5,6)
h <- c(3,5,7)
plot(x,y)
abline(y=h)

However I got error message:
Warning message: 
parameter "y" couldn't be set in high-level plot() function 
(I tried abline(h=y) , it;s not what I want also)

Do u know why?
 


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