nc_grid_to_dt_raw: Convert a netcdf array to long format as data.table (raw version)

Description

Extracts a variable from netcdf, similar to nc_grid_to_dt, but in a raw version. Requires more manual info, does not convert time units (like 'days since x'), and requires xy variables not dimensions (like a curvilinear grid).

Usage

nc_grid_to_dt_raw(
  filename,
  variable,
  var_t,
  var_x,
  var_y,
  has_time = TRUE,
  icell_raster_pkg = TRUE
)

Value

A data.table with columns icell (cell index), time (if has_time=T), value. Only if var_x and var_y supplied also x and y. Column names except icell are variable names as in the netcdf file.

Arguments

filename: Complete path to .nc file.
variable: Character, name of the variable to extract (required).
var_t: Character, name of the time variable. (recommended if has_time=TRUE)
var_x: (optional) Character, name of the x coordinate variable (not dimension!). If both var_x and var_y are supplied, results will have xy columns, too.
var_y: (optional) Character, name of the y coordinate variable (not dimension!). If both var_x and var_y are supplied, results will have xy columns, too.
has_time: Boolean, if TRUE (default), will read time information from file. Use FALSE, if file has no time dimension/variable.
icell_raster_pkg: Boolean, if TRUE, cell indices will be ordered as if you were extracting the data with the raster package. See also nc_grid_to_dt

Details

Names of netcdf variables can be inquired in a terminal with "ncdump -h", or in R for example using ncdf4::nc_open(filename).

Example use cases: netcdf file has issues with dimensions (no dimvar), time variable is in non-standard format.

Examples

Run this code

# example data
fn3 <- system.file("extdata", "test3.nc", package = "eurocordexr")
dat <- nc_grid_to_dt_raw(fn3, "tasmax", "Times")
str(dat)