Apply a function to subsets of layers of a SpatRaster (similar to
aggregate). The layers are combined based on the
The number of layers in the output SpatRaster equals the number of unique values in
index times the number of values that the supplied function returns for a single vector of numbers.
For example, if you have a SpatRaster with 6 layers, you can use
fun=sum. This will return a SpatRaster with two layers. The first layer is the sum of the first three layers in the input SpatRaster, and the second layer is the sum of the last three layers in the input SpatRaster. Indices are recycled such that
index=c(1,2) would also return a SpatRaster with two layers (one based on the odd layers (1,3,5), the other based on the even layers (2,4,6)).
The index can also be one of the following values to group by time period (if
x has the appropriate
time values): "years", "months", "yearmonths", "week" (the ISO 8601 week number, see Details), "yearweeks", "days", "doy" (day of the year), "7days" (seven-day periods starting at Jan 1 of each year), "10days", or "15days". It can also be a function that makes groups from time values.
Summary-methods if you want to use a more efficient function that returns multiple layers based on all layers in the SpatRaster.
# S4 method for SpatRaster tapp(x, index, fun, ..., cores=1, filename="", overwrite=FALSE, wopt=list())
factor or numeric (integer). Vector of length
nlyr(x) (shorter vectors are recycled) grouping the input layers. It can also be one of the following values: "years", "months", "yearmonths", "days", "week" (ISO 8601 week number), or "doy" (day of the year)
function to be applied. The following functions have been re-implemented in C++ for speed: "sum", "mean", "median", "modal", "which", "which.min", "which.max", "min", "max", "prod", "any", "all", "sd", "std", "first". To use the base-R function for say, "min", you could use something like
fun = \(i) min(i)
additional arguments passed to
positive integer. If
cores > 1, a 'parallel' package cluster with that many cores is created and used. You can also supply a cluster object. Ignored for functions that are implemented by terra in C++ (see under fun)
character. Output filename
filename is overwritten
list with named options for writing files as in
"week" follows the ISO 8601 definition. Weeks start on Monday. If the week containing 1 January has four or more days in the new year, then it is considered week "01". Otherwise, it is the last week of the previous year (week "52" or "53", and the next week is week 1.
r <- rast(ncols=10, nrows=10) values(r) <- 1:ncell(r) s <- c(r, r, r, r, r, r) s <- s * 1:6 b1 <- tapp(s, index=c(1,1,1,2,2,2), fun=sum) b1 #> class : SpatRaster #> dimensions : 10, 10, 2 (nrow, ncol, nlyr) #> resolution : 36, 18 (x, y) #> extent : -180, 180, -90, 90 (xmin, xmax, ymin, ymax) #> coord. ref. : lon/lat WGS 84 #> source(s) : memory #> names : X1, X2 #> min values : 6, 15 #> max values : 600, 1500 b2 <- tapp(s, c(1,2,3,1,2,3), fun=sum) b2 #> class : SpatRaster #> dimensions : 10, 10, 3 (nrow, ncol, nlyr) #> resolution : 36, 18 (x, y) #> extent : -180, 180, -90, 90 (xmin, xmax, ymin, ymax) #> coord. ref. : lon/lat WGS 84 #> source(s) : memory #> names : X1, X2, X3 #> min values : 5, 7, 9 #> max values : 500, 700, 900