How do I add the time to the netcdf file? - r

Question

I want to create a time series in a netcdf file with 3 dimensions(lon, lat, time[unlimited]). The timeseries should be created from other netcdf-files. Each of them have only one timepoint [For Example 17856].
I know how to create the new netcdf-file, how to extract the data from the netcdf-file as a 2D array and the time for the data.
My problem is:
How do I put the 2D array in the netcdf-file with its correct time? How does the start and count argument in the "ncvar_put" fucntion does work?
I use the ncdf4 package and read the Tutorial on:
http://geog.uoregon.edu/bartlein/courses/geog490/week04-netCDF.html#create-and-write-a-netcdf-file and searched for an answer but I still don`t understand it. I´m still unexperienced with netcdf files.
Example
e of my problem:
# data from other netcdf file
values = array(data = c(1:9)/10, dim = c(3,3))
values_2 = array(data = c(9:25)/10, dim = c(3,3))
time = 25
time_2 = 23
# set parameters
lon = 1:3
lat = 1:3
# define dimensions
# Longitude
londim = ncdim_def(name = "longitude", units = "degrees", vals = as.double(lon),
longname = "longitude")
# Latitude
latdim = ncdim_def(name = "latitude", units = "degrees", vals = as.double(lat),
longname = "latitude")
# Time
timedim = ncdim_def(name = "time", units ="days since 1582-10-15 00:00", vals = as.double(1),
unlim = TRUE, calendar = "gregorian")
# define variables
B01 = ncvar_def(name = "B01",
units ="percent",
list(londim,latdim,timedim),
missval = NA,
prec="double")
# create netcdf
nc_test = nc_create("test.nc", list(B01), force_v4 = TRUE)
# Add values
### Here is somethin missing --> How do I add the timestamp?
ncvar_put(nc_test, "B01", values, start=c(1,1,1), count=c(-1,-1,1))
ncvar_put(nc_test, "B01", values2, start=c(1,1,2), count=c(-1,-1,1))
When I want to extract the data I get the 3-3-2 array, but the timesteps are not correct, because I didnt add them. How do I do this?
I would like to have the 3-3-2 array and when I take the time and I want the right times in the correct order.

Answer 1

I add time to the netCDF file by using another method. This is the sample code for your reference.
from datetime import datetime
from datetime import timedelta
from netCDF4 import date2num
from netCDF4 import Dataset
import os
# generate time for netCDF with 1 hour interval
utc_now = datetime.utcnow()
time_list = [utc_now + timedelta(hours=1*step) for step in range(6)]
trans_time = date2num(time_list, units="hours since 0001-01-01 00:00:00.0", calendar="gregorian")
with Dataset(os.getcwd() + "/sample.nc", "w") as sample:
# Create dimension for sample.nc
time = sample.createDimension("time", None)
lat = sample.createDimension("lat", 3) # 3 is the latitude size in this sample
lon = sample.createDimension("lon", 3)
# Create variable for sample.nc
time = sample.createVariable("time","f8",("time",))
lat = sample.createVariable("lat","f4",("lat",))
lon = sample.createVariable("lon","f4",("lon",))
time[:] = trans_time
variable_with_time = sample.createVariable("variable_with_time", "f4", ("time", "lat", "lon"))
for key, value in sample.variables.items():
print(key)
print(value)
print("*"*70)
Output:
time
<class 'netCDF4._netCDF4.Variable'>
float64 time(time)
unlimited dimensions: time
current shape = (6,)
filling on, default _FillValue of 9.969209968386869e+36 used
**********************************************************************
lat
<class 'netCDF4._netCDF4.Variable'>
float32 lat(lat)
unlimited dimensions:
current shape = (3,)
filling on, default _FillValue of 9.969209968386869e+36 used
**********************************************************************
lon
<class 'netCDF4._netCDF4.Variable'>
float32 lon(lon)
unlimited dimensions:
current shape = (3,)
filling on, default _FillValue of 9.969209968386869e+36 used
**********************************************************************
variable_with_time
<class 'netCDF4._netCDF4.Variable'>
float32 variable_with_time(time, lat, lon)
unlimited dimensions: time
current shape = (6, 3, 3)
filling on, default _FillValue of 9.969209968386869e+36 used
**********************************************************************
You may notice that, time is placed as the first dimension. For detailed information, this is the link to the document that I referenced.