[R-sig-Geo] Error when I try to interpolate NA for each cell from Rasterstack

[Zhang Tianyi]

Dear all,

I need to substitute or interpolate the NA in a vector of each cell from a rasterstack data. I have two functions fun_sub for substituting NA and fun_interp for interpolating NA.
I found fun_sub works very well. But fun_interp does not work but I cannot find a reason.
Thank you very much

Tianyi Zhang

Below is a simple example:
#------EXAMPLE
library(timeSeries)
library(raster)
fun_sub <- function(x) {
  # substitute the NA to the mean of vector for each cell
  v=as.vector(x)
  z<-substituteNA(v,type="mean")
  return (z)
}

fun_interp <- function(x) {
  # interpolate the NA to the the linear regression of vector for each cell
  v=as.vector(x)
  z=interpNA(v, method="linear")
  return (z)
}

# create data
r<-raster(ncols=2,nrows=2)
r1<-r; r2<-r; r3<-r; r4<-r
r1[]<-c(1,1,1,2)
r2[]<-c(5,5,NA,5)
r3[]<-c(3,3,4,2)
r4[]<-c(6,5,5,2)
s<-stack(r1,r2,r3,r4)

# try the two functions; the task is change the NA in r2 to a number;
res_sub<-calc(s,fun_sub) # works great! substitute the NA to the mean of c(1,NA,4,5); I got c(1,3.333,4,5)
res_inter<-calc(s,fun_interp) # cannot interpolate; have an error, don't know the reason; I expected it is c(1, 2.5 ,4, 5). But it returns an error

# try whether interpNA() can work or not
interpNA(c(1,NA,4,5),method="linear") # but this function is OK.





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