Test era5 horly to monthly

inst/doc/usecase/ex2_11era5hourlyTomonthly.R

+library(startR)
+
+path <- '/esarchive/recon/ecmwf/era5/1hourly/$var$/$var$_$sdate$.nc'
+
+sdate <- sapply(1990:2019, function(x) paste0(x, sprintf('%02d', 1:12)))
+dim(sdate) <- c(month = 12, year = 30)
+
+data <- Start(dat = path,
+              var = 'tasmax',
+              sdate = sdate,
+              time = 'all',
+              latitude = indices(1:4),
+              longitude = indices(1:3),
+              #latitude = 'all',
+              #longitude = 'all', # when using this option, run Compute in Nord3.
+              split_multiselected_dims = TRUE,
+              synonims = list(longitude = c('lon', 'longitude'),
+                             latitude = c('lat', 'latitude')),
+              return_vars = list(latitude = 'dat',
+                                 longitude = 'dat',
+                                 time = 'sdate'),
+              retrieve = FALSE)
+
+Mean <- function(x) {
+  mean(x, na.rm = TRUE)
+}
+
+step <- Step(fun = Mean,
+             target_dims = c('time'),
+             output_dims = NULL)
+
+wf <- AddStep(data, step)
+  
+## locally
+start.time <- Sys.time()
+res1 <- Compute(wf,
+                chunks = list(year = 30))
+end.time <- Sys.time()
+time.taken <- end.time - start.time
+time.taken
+
+climatology <- s2dv::MeanDims(result, 'year') 
+
+plot(1:(12*30), s2dv::MeanDims(result, c('latitude', 'longitude')),
+     type = 'b',  ylab = "tasmax (Celsius)", xlab = "Time (months)",
+     xaxt = 'n', bty = 'n')
+lines(1:(12*30), rep(s2dv::MeanDims(climatology, c('latitude', 'longitude')), 30),
+      col = 'purple')
+axis(1, seq(6, 360, 12), 1990:2019)
+
+## efficiency tests can be done comparing against and submitting to Nord3:
+start.time <- Sys.time()
+res1 <- Compute(wf,
+                chunks = list(year = 30, month = 12))
+end.time <- Sys.time()
+time.taken <- end.time - start.time
+time.taken
+