# Estimate values for cell values that are `NA`

by interpolating between layers

`approximate.Rd`

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`

## Usage

```
# S4 method for 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`

## Examples

```
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))
```