Given a data frame with fields x, y and z, df.to.mat uses the x and
y coordinates to rearrange z into a rectangular matrix image Z.
Usage
df.to.mat(df)
Value
matrix image
Arguments
df
data frame with fields x, y and z
Details
This function requires that all pixels in the image are defined, that is df$x and df$y must be the
column outputs of the function expand.grid(x0,y0) where x0, y0 are axes values. Note that x0 and
y0 do not need to be regularly spaced.