# Estimate values for cell values that are `NA` by interpolating between layers approximate uses the `stats` function `approx` to estimate values for cells that are `NA` by interpolation across layers. Layers are considered equidistant, unless argument `z` is used, or `time(x)` returns values that are not `NA`, in which case these values are used to determine distance between layers. For estimation based on neighboring cells see `focal` methods ```r ## S4 method for signature 'SpatRaster' approximate(x, method="linear", yleft, yright, rule=1, f=0, ties=mean, z=NULL, NArule=1,filename="", ...) ``` ## Arguments - `x`: SpatRaster - `method`: specifies the interpolation method to be used. Choices are "linear" or "constant" (step function; see the example in `approx` - `yleft`: the value to be returned before a non-`NA` value is encountered. The default is defined by the value of rule given below - `yright`: the value to be returned after the last non-`NA` value is encountered. The default is defined by the value of rule given below - `rule`: an integer (of length 1 or 2) describing how interpolation is to take place at for the first and last cells (before or after any non-`NA` values are encountered). If rule is 1 then NAs are returned for such points and if it is 2, the value at the closest data extreme is used. Use, e.g., `rule = 2:1`, if the left and right side extrapolation should differ - `f`: for method = "constant" a number between 0 and 1 inclusive, indicating a compromise between left- and right-continuous step functions. If y0 and y1 are the values to the left and right of the point then the value is `y0*(1-f)+y1*f` so that `f = 0)` is right-continuous and `f = 1` is left-continuous - `ties`: Handling of tied 'z' values. Either a function with a single vector argument returning a single number result or the string "ordered" - `z`: numeric vector to indicate the distance between layers (e.g., depth). The default is `time(x)` if these are not `NA` or else `1:nlys(x)` - `NArule`: single integer used to determine what to do when only a single layer with a non-`NA` value is encountered (and linear interpolation is not possible). The default value of 1 indicates that all layers will get this value for that cell; all other values do not change the cell values - `filename`: character. Output filename - `...`: additional arguments for writing files as in `writeRaster` ## Returns SpatRaster ## See Also `focal`, `fillTime` ## Examples ```r r <- rast(ncols=5, nrows=5) r1 <- setValues(r, runif(ncell(r))) r2 <- setValues(r, runif(ncell(r))) r3 <- setValues(r, runif(ncell(r))) r4 <- setValues(r, runif(ncell(r))) r5 <- setValues(r, NA) r6 <- setValues(r, runif(ncell(r))) r1[6:10] <- NA r2[5:15] <- NA r3[8:25] <- NA s <- c(r1,r2,r3,r4,r5,r6) s[1:5] <- NA x1 <- approximate(s) x2 <- approximate(s, rule=2) x3 <- approximate(s, rule=2, z=c(1,2,3,5,14,15)) ```

approximate function