Useful functions

dropna(ds, varname, nanval)	Drop values corrresponding to NaN (marthe convention, eg.
fillna(ds, varname, value)	Replace real nan (np.nan) value in dataset[varname], edge case of gridmarthe.replace()
subset(ds, varname, value)	Subset dataset based on variable name and value.
replace(ds, varname, value, replace)	Replace a value in xr.Dataset for a variable
assign_coords(ds[, add_lay, coords, ...])	Assign coordinates from variables to dimensions
stack_coords(ds[, coords, dropna])	Transform a 3 or 4D aray into 1 or 2D array inverse of assign_coords()
read_dates_from_pastp(fpastp[, encoding])	Read simulation timesteps from a .pastp file