Speedy Raster Value Substitution

A fast data.table-based alternative to raster::subs().

Usage

subsDT(x, dict, by = 1, which = 2, subsWithNA = TRUE, filename = "", ...)

Arguments

x

Categorical RasterLayer with integer values giving field class.

dict

A data.frame or data.table with one (or possibly more) columns corresponding to the values of cells in x and one (or possibly more) columns giving the value to which each value in x should be mapped.

by

Vector of one or possibly more integers or character strings giving the indices or names of the column in dict containing the categorical values in x.

which

Vector of one or possibly more integers or character strings giving the indices or names of the column in dict with the numerical values to which each value in by should be mapped.

subsWithNA

Logical. If TRUE values that are not matched become NA. If FALSE, they retain their original value (which could also be NA). This latter option is handy when you want to replace only one or a few values. It cannot be used when x has multiple layers

filename

Character string giving (optional) file name to which the resultant raster should be written.

...

Additional arguments as for raster::writeRaster(), on which this function relies.

Value

A RasterLayer object.

Author

Joshua O'Brien

Examples

r <- raster(ncol = 10, nrow = 10)
r[] <- round(runif(ncell(r)) * 10)
df <- data.frame(id = 2:8, v = c(10, 10, 11, 11, 12:14))
x <- subsDT(r, df)
x2 <- subsDT(r, df, subsWithNA = FALSE)

df$v2 <- df$v * 10
x3 <- subsDT(r, df, which = 2:3)

s <- stack(r, r*3)
names(s) <- c("first", "second")
x4 <- subsDT(s, df)
x5 <- subsDT(s, df, which = 2:3)