Obtaining mean of rasters

Question

I want to get a mean chlorophyll a from the 3 .nc files below, and am wondering if using mosaic is the correct thing to do?

https://oceandata.sci.gsfc.nasa.gov/cgi/getfile/AQUA_MODIS.20020101_20021231.L3m.YR.NSST.sst.4km.nc https://oceandata.sci.gsfc.nasa.gov/cgi/getfile/AQUA_MODIS.20030101_20031231.L3m.YR.NSST.sst.4km.nc https://oceandata.sci.gsfc.nasa.gov/cgi/getfile/AQUA_MODIS.20040101_20041231.L3m.YR.NSST.sst.4km.nc

library(terra)

#List of .nc files in directory
fls <- list.files("/folder/with/files", ".nc$", full.names = TRUE)

#list of rast objects
r_list <- lapply(fls, rast)

#create spatial raster collection
coll <- sprc(r_list)

#Get the mean values across all rasters
chla_m<-mosaic(coll, fun="mean")

Answer 1

You can use the following code

library(terra)

#List of .nc files in directory
fls <- list.files("/folder/with/files", ".nc$", full.names = TRUE)

#list to SpatRaster object conversion
r_list <- rast(fls)

#For global mean calculation i.e. single mean for the entire SpatRaster
global(r_list, mean, na.rm=TRUE)

#For local mean calculation i.e. pixel-wise mean calculation
mean(r_list, na.rm=TRUE)