I  have this data set that both x & y are ordered vectors of length 600 & 700 
respectively; z is a 600 by 700 matrix whose entry z[i,j] is either a missing 
value (indicated by 'NaN') or a real number between 0 and 1.  The contour 
function 

contour(x,y,z) 

gives me a blank picture. I guess the reason is that most of z-entries are 
missing, only less than 1% are non missing. 

Question (1) 

Is there a way that I could manipulate the data or function to have the 
non-missing values plotted?

Also, trying function "persp" gives me this error message

persp(x,y,z) 

Error in persp.default(x, y, z) : invalid 'z' limits

I look at the manual of "persp". I guess, the error message comes from its 
internal call

zlim = range(z, na.rm = TRUE)

it appears to me that "persp" can't handle missing value yet its manual states 
clearly

z: a matrix containing the values to be plotted ('NA's are
          allowed).  Note that ā€˜xā€™ can be used instead of ā€˜zā€™
          for convenience.


Question (2)

Can "persp" handle missing values in z? if the answer is a  sounding "yes", how 
should I do in my case? 

Please help, Thanks!

Your frustrated

Andrew




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