R/scQC.R

In rPanglaoDB: Download and Merge Single-Cell RNA-Seq Data from the PanglaoDB Database

#' @import Matrix
#' @importFrom stats lm predict
scQC <- function(X, mtThreshold = 0.1, minLSize = 1000){
  if(class(X) == 'Seurat'){
    countMatrix <- X@assays$RNA@counts
  } else {
    countMatrix <- X
  }
  librarySize <- colSums(countMatrix)
  countMatrix <- countMatrix[,librarySize >= minLSize]
  librarySize <- colSums(countMatrix)
  mtGenes <- grep('^MT-',toupper(rownames(countMatrix)))
  nGenes <- colSums(countMatrix != 0)

  genesLM <- lm(nGenes~librarySize)
  genesLM <- as.data.frame(predict(genesLM, data.frame(librarySize), interval = 'prediction'))

  if(isTRUE(length(mtGenes) > 0)){
    mtCounts <- colSums(countMatrix[grep('^MT-',toupper(rownames(countMatrix))),])
    mtProportion <- mtCounts/librarySize
    mtLM <- lm(mtCounts~librarySize)
    mtLM <- as.data.frame(predict(mtLM, data.frame(librarySize), interval = 'prediction'))
    selectedCells <- ((mtCounts > mtLM$lwr) & (mtCounts < mtLM$upr) & (nGenes > genesLM$lwr) & (nGenes < genesLM$upr) & (mtProportion <= mtThreshold) & (librarySize < (2 * mean(librarySize))))
  } else {
    selectedCells <- ((nGenes > genesLM$lwr) & (nGenes < genesLM$upr) & (librarySize < (2 * mean(librarySize))))
  }
  selectedCells <- colnames(countMatrix)[selectedCells]
  if(class(X) == 'Seurat'){
    X <- subset(X, cells = selectedCells)
  } else {
    X <- countMatrix[,selectedCells]
  }
  return(X)
}