# approxNA: Estimate values for cell values that are 'NA' by... In raster: Geographic Data Analysis and Modeling

## Description

approxNA uses the `stats` function `approx` to estimate values for cells that are `NA` by interpolation across layers. Layers are considered equidistant, unless an argument 'z' is used, or `getZ` returns values, in which case these values are used to determine distance between layers.

For estimation based on neighbouring cells see `focal`

## Usage

 ```1 2 3``` ```## S4 method for signature 'RasterStackBrick' approxNA(x, filename="", method="linear", yleft, yright, rule=1, f=0, ties=mean, z=NULL, NArule=1, ...) ```

## Arguments

 `x` RasterStack or RasterBrick object `filename` character. Output filename (optional) `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., time, depth). The default is 1:nlayers(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 `...` additional arguments as for `writeRaster`

## Value

RasterBrick

` focal`
 ``` 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15``` ```r <- raster(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 <- stack(r1,r2,r3,r4,r5,r6) s[1:5] <- NA x1 <- approxNA(s) x2 <- approxNA(s, rule=2) x3 <- approxNA(s, rule=2, z=c(1,2,3,5,14,15)) ```