R, mapply , ggplot : EXPR must be a length 1 vector

Question

I am trying plot the subsets of a table using ggplot and gridExtra. But I have bumbed in the following error EXPR must be a length 1 vector.

I could come up with any si

Answer 1

Change

mplot <- mapply(p,dt2[,zone1],dt2[,zone2])

to

mplot <- mapply(p,dt2[,zone1],dt2[,zone2], SIMPLIFY=FALSE)

or

mplot <- Map(p,dt2[,zone1],dt2[,zone2])

mapply() will attempt to coerce it's result to a matrix if the dimensions of the returned objects match up, however, in this case you will always want a list. You can either set the SIMPLIFY= parameter to false, or use Map() which always returns a list.