defaultDrops: Call cells from their total number of UMIs

In MarioniLab/DropletUtils: Utilities for Handling Single-Cell Droplet Data

Call cells from their total number of UMIs

Description

Call cells according to the number of UMIs associated with each barcode, as implemented in CellRanger version 2.

Usage

defaultDrops(m, ...)

## S4 method for signature 'ANY'
defaultDrops(m, expected = 3000, upper.quant = 0.99, lower.prop = 0.1)

## S4 method for signature 'SummarizedExperiment'
defaultDrops(m, ..., assay.type = "counts")

Arguments

m	A numeric matrix-like object containing counts, where columns represent barcoded droplets and rows represent features. The matrix should only contain barcodes for an individual sample, prior to any filtering for cells. Alternatively, a SummarizedExperiment containing such a matrix.
...	For the generic, further arguments to pass to individual methods. For the SummarizedExperiment method, further arguments to pass to the ANY method.
expected	A numeric scalar specifying the expected number of cells in this sample, as specified in the call to CellRanger.
upper.quant	A numeric scalar between 0 and 1 specifying the quantile of the top expected barcodes to consider for the first step of the algorithm.
lower.prop	A numeric scalar between 0 and 1 specifying the fraction of molecules of the upper.quant quantile result that a barcode must exceed to be called as a cell.
assay.type	Integer or string specifying the assay containing the count matrix.

Details

The defaultDrops function will call cells based on library size similarly to the CellRanger software suite from 10X Genomics. Default arguments correspond to an exact reproduction of CellRanger's algorithm, where the number of expected cells was also left at CellRanger default value.

The method computes the upper.quant quantile of the top expected barcodes, ordered by decreasing number of UMIs. Any barcodes containing more molecules than lower.prop times this quantile is considered to be a cell, and is retained for further analysis.

This method may be vulnerable to calling very well-captured background RNA as cells, or missing real cells with low RNA content. See ?emptyDrops for an alternative approach for cell calling.

Value

A logical vector of length ncol(m), indicating whether each column of m was called as a cell.

Author(s)

Jonathan Griffiths

References

10X Genomics (2017). Cell Ranger Algorithms Overview. https://support.10xgenomics.com/single-cell-gene-expression/software/pipelines/latest/algorithms/overview

See Also

emptyDrops, for another method for calling cells.

Examples

# Mocking up some data:
set.seed(0)
my.counts <- DropletUtils:::simCounts()

# Identify likely cell-containing droplets.
called <- defaultDrops(my.counts)
table(called)

# Get matrix of called cells.
cell.counts <- my.counts[, called]

MarioniLab/DropletUtils documentation built on Dec. 13, 2024, 6:13 a.m.