Hello, This is probably really simple but I can't work out how to change my cluster IDs from their numbers to a cell type. ie, cluster "1" to "T cell", for example. I used scran for my clustering:

g <- buildSNNGraph(sce, use.dimred="PCA")

cluster <- igraph::cluster_louvain(g)$membership

colLabels(sce) <- factor(cluster) table(colLabels(sce))

Can someone please help me? 🙏🙏🙏

It's really just a simple matching operation:

suppressPackageStartupMessages(library(SingleCellExperiment))

#/ example data
ncells <- 100
u <- matrix(rpois(20000, 5), ncol=ncells)
sce <- SingleCellExperiment(assays=list(counts=u))
sce$cluster <- factor(sample(c(1:4), size=ncells, replace=TRUE))
colData(sce)
#> DataFrame with 100 rows and 1 column
#>      cluster
#>     <factor>
#> 1          1
#> 2          1
#> 3          4
#> 4          3
#> 5          4
#> ...      ...
#> 96         3
#> 97         4
#> 98         1
#> 99         1
#> 100        2

#/ make a translation table
translation <- data.frame(cluster=factor(c(1:4)),
                          replacement=c("Tcell", "Bcell", "NKcell", "Macrophage"))

translation
#>   cluster replacement
#> 1       1       Tcell
#> 2       2       Bcell
#> 3       3      NKcell
#> 4       4  Macrophage

#/ now match colData against translation
matched <- match(sce$cluster, translation$cluster)

#/ translate
translated <- translation[matched,]$replacement

#/ feed that back into the sce
sce$translated <- factor(translated)

colData(sce)
#> DataFrame with 100 rows and 2 columns
#>      cluster translated
#>     <factor>   <factor>
#> 1          1 Tcell     
#> 2          1 Tcell     
#> 3          4 Macrophage
#> 4          3 NKcell    
#> 5          4 Macrophage
#> ...      ...        ...
#> 96         3 NKcell    
#> 97         4 Macrophage
#> 98         1 Tcell     
#> 99         1 Tcell     
#> 100        2 Bcell
Created on 2022-08-05 by the reprex package (v2.0.1)

You can use other functions rather than match to match the two data.frames such as dplyr::left_join as long as that preserves the order of the clusters in sce$cluster.