[R] lines.formula with subset

[John Field]

Dear list,

When I try to use lines.formula with subset and another argument I 
get an error.
e.g.

x<-1:5
y<-c(1,3,NA,2,5)
plot(y~x, type="n")  # set up frame
lines(y~x, subset=!is.na(y))  # works OK
lines(y~x, type="o", col="blue")  # works OK
# but
lines(y~x, subset=!is.na(y), col="red")  # gives an error:

Error in if (length(x) == l) x[s] else x : argument is of length zero

Why does this happen?

With thanks,
John

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