issue mosaicing images with the same name in R

Question

hello i have 4 folders containing modis images each folder have time series images named the same way e.g:

Folder 1 :
MCD19A2_Optical_Depth_047_2019_032.tif
MCD19A2_Optical_Depth_047_2019_033.tif
MCD19A2_Optical_Depth_047_2019_034.tif
MCD19A2_Optical_Depth_047_2019_035.tif
MCD19A2_Optical_Depth_047_2019_036.tif
MCD19A2_Optical_Depth_047_2019_037.tif
...

Folder 2 :
MCD19A2_Optical_Depth_047_2019_032.tif
MCD19A2_Optical_Depth_047_2019_033.tif
MCD19A2_Optical_Depth_047_2019_034.tif
MCD19A2_Optical_Depth_047_2019_035.tif
MCD19A2_Optical_Depth_047_2019_036.tif
MCD19A2_Optical_Depth_047_2019_037.tif
...

Folder 3 :
MCD19A2_Optical_Depth_047_2019_032.tif
MCD19A2_Optical_Depth_047_2019_033.tif
MCD19A2_Optical_Depth_047_2019_034.tif
MCD19A2_Optical_Depth_047_2019_035.tif
MCD19A2_Optical_Depth_047_2019_036.tif
MCD19A2_Optical_Depth_047_2019_037.tif
...

Folder 4 :
MCD19A2_Optical_Depth_047_2019_032.tif
MCD19A2_Optical_Depth_047_2019_033.tif
MCD19A2_Optical_Depth_047_2019_034.tif
MCD19A2_Optical_Depth_047_2019_035.tif
MCD19A2_Optical_Depth_047_2019_036.tif
MCD19A2_Optical_Depth_047_2019_037.tif
...

i would like to know how to mosaic the 4 modis images MCD19A2_Optical_Depth_047_2019_032.tif together and the 4 MCD19A2_Optical_Depth_047_2019_033.tif together in R ...

with the normal gregorian calendar dates in the names not as above in the julian day

Answer 1

It is better if you post some code you have tried so one could make a better suggestion. I think you could try something like:

dirNames <- c(paste('Folder', 1:4))
filesNames <- c("MCD19A2_Optical_Depth_047_2019_032.tif",
                "MCD19A2_Optical_Depth_047_2019_033.tif",
                "MCD19A2_Optical_Depth_047_2019_034.tif",
                "MCD19A2_Optical_Depth_047_2019_035.tif",
                "MCD19A2_Optical_Depth_047_2019_036.tif",
                "MCD19A2_Optical_Depth_047_2019_037.tif", 
                "MCD19A2_Optical_Depth_047_2019_038.tif")

filesRast <- stringr::str_c(rep(dirNames, length(filesNames)), 
                            '/', filesNames)

filesFolders <-lapply(dirNames, 
                      function(x) {
                        y <- filesRast[stringr::str_detect(pattern = x, string = filesRast)]
                        y <- sort(y)
                        })

for(i in 1:length(dirNames)){
  name <- lapply(filesFolders, function(x) x[i])
  dateOrig <- gsub('_', '',gsub(paste0('.*MCD19A2_Optical_Depth_047_|.tif'), '', name[1]))
  dateGreg <- as.Date(dateOrig, "%y%j")
  r <- raster::raster(name[1])
  for(j in 2:length(name)){
    r <- raster::mosaic(r, raster::raster(name[i]))
  }
  raster::writeRaster(r, paste0('out/folder/', 'MCD19A2_mosaic_', dateGreg, '.tif'))
}

Note that filesNames is a character vector I copied from your example. Buy you should use something like list.files('/folder/where/tif/are', pattern='.tif$'), to extract all the names in your folders.