如何在R中为HDF文件编写循环？

Question

I have more than 1,000 MODIS HDF images in a folder:

M:\join

Their name shows us which HDF files are belong to a certain date and must be mosaiced together.

For example, in the below, 2009090 means these three images are belong to the same date and must be mosaiced together:

MOD05_L2.A2009090.0420.051.2010336084010
MOD05_L2.A2009090.0555.051.2010336100338
MOD05_L2.A2009090.0600.051.2010336100514

Or these two, are for the same date, 2009091 :

MOD05_L2.A2009091.0555.051.2010336162871
MOD05_L2.A2009091.0600.051.2010336842395

Right now, I am able to successfully use mosaicHDF () to mosaic them for one date as below:

hdfs <- c('MOD05_L2.A2009090.0420.051.2010336084010.hdf',
          'MOD05_L2.A2009090.0555.051.2010336100338.hdf',
          'MOD05_L2.A2009090.0600.051.2010336100514.hdf')

mosaicHDF(hdfNames=hdfs, filename='newhdf.hdf', MRTpath='C:/MRT/bin',bands_subset="1 0 0 0", delete=FALSE) 

Since, there are more than 1,000 HDF files for 1 year in the folder, how should I write a loop to use such function for all HDF files, and make a mosaic file for each date?

I would be very grateful if anyone could help me.

Thanks.

Answer 1

Group the files by their ID using grep , and then use a for loop to create the mosaic for each group:

fnames <- c("MOD05_L2.A2009090.0420.051.2010336084010", "MOD05_L2.A2009090.0555.051.2010336100338", "MOD05_L2.A2009090.0600.051.2010336100514", "MOD05_L2.A2009091.0555.051.2010336162871", "MOD05_L2.A2009091.0600.051.2010336842395")
#or
fnames <- list.files(path = "M:/join/", pattern = "*.hdf") #Credits do @Gregor for noticing this

ids <- unique(substr(fnames, 10, 17))

groups <- sapply(ids, grep, fnames, value=TRUE)

for (gr in seq_along(groups)) {
  mosaicHDF(hdfNames=groups[[gr]], filename=paste0(names(groups)[gr], '.hdf'), 
            MRTpath='C:/MRT/bin',bands_subset="1 0 0 0", delete=FALSE)
}

This should save all the mosaic files for each group, with the file name as the group ID.

Answer 2

    fnames <- c("MOD05_L2.A2009090.0420.051.2010336084010", "MOD05_L2.A2009090.0555.051.2010336100338", "MOD05_L2.A2009090.0600.051.2010336100514", "MOD05_L2.A2009091.0555.051.2010336162871", "MOD05_L2.A2009091.0600.051.2010336842395")
    #or
    fnames <- list.files(path = "M:/join/", pattern = "*.hdf") #Credits do @Gregor for noticing this

    ids <- unique(substr(fnames, 10, 17))

    groups <- lapply(ids, grep, fnames, value=TRUE)  # This line should be lapply instead of sapply
    ref.num = substr(groups[[j]][1], 10, 17) #Give output different names


for (gr in seq_along(groups)) {
ref.num = substr(groups[[gr]][1], 10, 17) 
      mosaicHDF(hdfNames=groups[[gr]], filename=paste0("MOD05_",ref.num, ".hdf"), 
                MRTpath='C:/MRT/bin',bands_subset="1 0 0 0", delete=FALSE)
    }