Does `.view$as_HDF5AnnData(file = subset_file_path)` copy all data to the memory before writing to the disk?

[PedroMilanezAlmeida]

Topic Area

Reading/writing H5AD files

Your Question

I have a large h5ad file read as HDF5AnnData.

I subset and reordered it and now I have a AnnDataView.

I want to write to a new file.

Pseudocode:

# access h5ad keeping data on disk
h5ad <- 
  anndataR::read_h5ad(
    path = file_path,
    as = "HDF5AnnData")

# some subetting and reordering creating AnnDataView
h5ad <- h5ad[reord_subsetting_cells_vec,reord_subsetting_genes_vec]

h5ad <- 
  h5ad$as_HDF5AnnData(file = subset_file_path)

My question is, how memory efficient is the h5ad$as_HDF5AnnData(file = subset_file_path) operation? Does it happen in chunks? Do all data get copied to memory first and then get written to the disk?

Any help would be much appreciated.