persp() problem

Dear friends. A very humble admirer of the progress of R with a very

simple problem. I have the data shown below

month  day   year  dosis  vanco
12 31 1999 1 3.8
1 3 2000 1 2.4
1 7 2000 1 3.4
1 12 2000 2 7.1
1 14 2000 2 5.3
1 17 2000 2 5.7
1 19 2000 3 7.7
1 21 2000 3 8.3
1 24 2000 4 8.7
1 26 2000 4 11.1
1 31 2000 4 12.3
2 7 2000 4.5 12.0
2 14 2000 4.5 14.9
2 18 2000 4.5 23.0
2 25 2000 3 20.1
2 28 2000 2 11.3

dates <- mdy.date(month,day,year)
persp(dosis,dates,vanco)
-- trying to produce a three demensional picture of vancomycin versus dose

and data.

but: Error in persp(dosis, dates, vanco) : increasing x and y values expected
Dates is increaing, and I couldnot figure out how to make both dosis and

dates increase and wonder

how to produce a surface in this situation.

Dear Troels,

Sure it won't work. The help file ?persp says:

    x, y: locations of grid lines at which the values in `z' are
          measured.  These must be in ascending order.  By default,
          equally spaced values from 0 to 1 are used.  If `x' is a
          `list', its components `x$x' and `x$y' are used for `x' and
          `y', respectively.

       z: a matrix containing the values to be plotted (`NA's are
          allowed).  Note that `x' can be used instead of `z' for
          convenience.


So in your case, vanco must be a matrix. If you do the following:


y <- c(1,2,3,4,4.5)  # the 5 levels of dosis
z <- matrix(data=NA, nrow=length(dates), ncol=length(y))
for (i in 1:length(dates))
{
  j <- which(y == dosis[i])  # get the index of y which value is equal to
the dose
  z[i,j] <- vanco[i]
}

then you get:

z

[,1] [,2] [,3] [,4] [,5]
 [1,]  3.8   NA   NA   NA   NA
 [2,]  2.4   NA   NA   NA   NA
 [3,]  3.4   NA   NA   NA   NA
 [4,]   NA  7.1   NA   NA   NA
 [5,]   NA  5.3   NA   NA   NA
 [6,]   NA  5.7   NA   NA   NA
 [7,]   NA   NA  7.7   NA   NA
 [8,]   NA   NA  8.3   NA   NA
 [9,]   NA   NA   NA  8.7   NA
[10,]   NA   NA   NA 11.1   NA
[11,]   NA   NA   NA 12.3   NA
[12,]   NA   NA   NA   NA 12.0
[13,]   NA   NA   NA   NA 14.9
[14,]   NA   NA   NA   NA 23.0
[15,]   NA   NA 20.1   NA   NA
[16,]   NA 11.3   NA   NA   NA

though the help says that NA's are allowed, I am not sure that persp() can
deal with such an incomplete matrix. Indeed, I tried:

persp(dates,y,z)

which yielded an empty box. Probably persp() is not the appropriate
function to visualize your data.

Best,

Emmanuel Paradis

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