BPCells matrices can be interconverted with Matrix package dgCMatrix sparse matrices, as well as base R dense matrices (though this may result in high memory usage for large matrices)

## Usage

```
# Convert to R from BPCells
as(bpcells_mat, "dgCMatrix") # Sparse matrix conversion
as.matrix(bpcells_mat) # Dense matrix conversion
# Convert to BPCells from R
as(dgc_mat, "IterableMatrix")
```