Tidyverse

If you ask me: what’s your favorite machine learning algorithm? I would answer logistic regression (with regularization: Lasso, Ridge and Elastic) followed by random forest. In fact, that’s how we try those methods in order. Deep learning can perform well for tabular data with complicated architecture while random forest or boost tree based method usually work well out of the box. Regression and random forest are more interpretable too.

Load libraries library(dplyr) library(Seurat) library(patchwork) library(ggplot2) library(ComplexHeatmap) library(SeuratData) set.seed(1234) prepare the data data("pbmc3k") pbmc3k #> An object of class Seurat #> 13714 features across 2700 samples within 1 assay #> Active assay: RNA (13714 features, 0 variable features) ## routine processing pbmc3k<- pbmc3k %>% NormalizeData(normalization.method = "LogNormalize", scale.factor = 10000) %>% FindVariableFeatures(selection.method = "vst", nfeatures = 2000) %>% ScaleData() %>% RunPCA(verbose = FALSE) %>% FindNeighbors(dims = 1:10, verbose = FALSE) %>% FindClusters(resolution = 0.

Single cell matrix is often represented as gene x cell in R/Seurat, but it is represented as cell x gene in python/scanpy. Let’s use a real example to show how to transpose between the two formats. The GEO accession page is at https://www.ncbi.nlm.nih.gov/geo/query/acc.cgi?acc=GSE154763 Download the data We can use command line to download the count matrix at ftp: https://ftp.ncbi.nlm.nih.gov/geo/series/GSE154nnn/GSE154763/suppl/ wget https://ftp.ncbi.nlm.nih.gov/geo/series/GSE154nnn/GSE154763/suppl/GSE154763_ESCA_normalized_expression.csv.gz -O ~/blog_data/GSE154763_ESCA_normalized_expression.csv.gz # decompress the file gunzip GSE154763_ESCA_normalized_expression.csv.gz # this GEO matrix is cell x gene # take a look by https://www.

It is very common to see in the scRNAseq papers that the authors compare cell type abundance across groups (e.g., treatment vs control, responder vs non-responder). Let’s create some dummy data. library(tidyverse) set.seed(23) # we have 6 treatment samples and 6 control samples, 3 clusters A,B,C # but in the treatment samples, cluster C is absent (0 cells) in sample7 sample_id<- c(paste0("sample", 1:6, "_control", rep(c("_A","_B","_C"),each = 6)), paste0("sample", 8:12, "_treatment", rep(c("_A","_B", "_C"), each = 5))) sample_id<- c(sample_id, "sample7_treatment_A", "sample7_treatment_B") cell_id<- paste0("cell", 1:20000) cell_df<- tibble::tibble(sample_id = sample(sample_id, size = length(cell_id), replace = TRUE), cell_id = cell_id) %>% tidyr::separate(sample_id, into = c("sample_id", "group", "clusterid"), sep= "") cell_num<- cell_df %>% group_by(group, cluster_id, sample_id)%>% summarize(n=n()) cell_num ## # A tibble: 35 x 4 ## # Groups: group, cluster_id [6] ## group cluster_id sample_id n ## <chr> <chr> <chr> <int> ## 1 control A sample1 551 ## 2 control A sample2 546 ## 3 control A sample3 544 ## 4 control A sample4 585 ## 5 control A sample5 588 ## 6 control A sample6 542 ## 7 control B sample1 550 ## 8 control B sample2 562 ## 9 control B sample3 574 ## 10 control B sample4 563 ## # … with 25 more rows total_cells<- cell_df %>% group_by(sample_id) %>% summarise(total = n()) total_cells ## # A tibble: 12 x 2 ## sample_id total ## <chr> <int> ## 1 sample1 1673 ## 2 sample10 1713 ## 3 sample11 1691 ## 4 sample12 1696 ## 5 sample2 1633 ## 6 sample3 1700 ## 7 sample4 1711 ## 8 sample5 1768 ## 9 sample6 1727 ## 10 sample7 1225 ## 11 sample8 1720 ## 12 sample9 1743 join the two dataframe to get percentage of cells per cluster per sample