Convert a List to .loom File in R for scVelo

Question

[630720255]

Hi there, currently I'm doing some trajectory analysis with scVelo and velocyto for some 10X single cell data, which involved in some data integration and barcode relocation process.

I use the read.loom.matrices function to read about 10 to 20 different .loom files in turn, which gives me a huge list, each element of this list contains 3 lists "spliced" "unspliced" "ambiguous", and I did the data processing and integration with R, finally I get a new integrated list which only contains "spliced" "unspliced" "ambiguous" matrices.

My question is, I still have no idea how to convert this final list into .loom file as readable anndata for scVelo in a good way by R. I tried the as.Seurat %>% as.loom, but seems that the layer construction was significant different with the original .loom file. Any income will be much appraciated. Thanks!

Answer 1

[630720255]

OK I've figured it out anyway ... I would like to write my solution here for recording and any possible incomes.

What you need is several .loom files that contain velocity info, and a related seurat object which have already been integrated.

First you will need to read those .loom files (e.g. read.loom.matrices) as a list, each element of this list contains 3 elements :spliced, unspliced, and ambiguous. Then you need to change colnames of each sub element along with colnames of your seurat object. The merging process of this list could be done as a simple lapply function with do.call(cbind), after that you will get a new list which contains spliced, unspliced, and ambiguous dgmatirx.

For scVelo, use the as.Seurat(x = ldat) to convert the ldat list into the Seurat format (e.g., seu.new), then change the seu.new[["RNA"]] slot to the [["spliced"]] slot and set as the default assay slot with DefaultAssay function. Load what you will need (e.g., [["umap"]] or $seurat_clusters slot) into the seu.new object.

Finally, convert it into H5AD format with SaveH5Seurat and Convert function, which could be read by scanpy in python.

best, W