fix bug

SelectNetworkGenes <- function(

  seurat_obj,

  gene_select="variable", fraction=0.05,

  n_chunks = 5, # for binarizing the exp matrix. This can be increased to save memory

  group.by=NULL, # should be a column in the Seurat object, eg clusters

  gene_list=NULL, wgcna_name=NULL

 ){

    # binarize counts matrix in chunks to save memory

    expr_mat <- GetAssayData(seurat_obj, slot='counts')

    n_chunks <- ceiling(ncol(expr_mat) / 10000)

    chunks <- cut(1:nrow(expr_mat), n_chunks)

    expr_mat <- do.call(rbind, lapply(levels(chunks), function(x){

      print(x)

      cur <- expr_mat[chunks == x,]

      cur[cur > 0] <- 1

      cur

    group_gene_list <- list()

    if(!is.null(group.by)){

      # identify genes that are expressed

      print(group.by)

      groups <- unique(seurat_obj@meta.data[[group.by]])

      for(cur_group in groups){