How to merge cell type from subsetted seurat object to main seurat object?

[Jiayi-Zheng]

I have a seurat object seu with many cells, and for convenience I subset part of the cells into a new seurat called seu_sub1

Now that I've identified the cell types for cells in seu_sub1, and annotated them via RenameIdents(), I want to merge it back to seu, with those from seu_sub1 retain their name in [email protected], while the remaining unidentified clusters in seu to remain with the cluster number they were assigned with.

Somehow I'm having quite some trouble performing this (should be) simple task... currently I'm trying to extract both active.ident with cell barcode to two dataframe and combine them together before importing it back to seu...

I am wondering if there is a quicker way for that?