perFeatureQCMetrics {scater} | R Documentation

## Per-feature quality control metrics

### Description

Compute per-feature quality control metrics for a count matrix or a SummarizedExperiment.

### Usage

    perFeatureQCMetrics(x, ...)

    ## S4 method for signature 'ANY'
    perFeatureQCMetrics(
      x,
      subsets = NULL,
      detection_limit = 0,
      BPPARAM = SerialParam(),
      flatten = TRUE
    )

    ## S4 method for signature 'SummarizedExperiment'
    perFeatureQCMetrics(x, ..., exprs_values = "counts")

### Arguments

`x` | A numeric matrix of counts with cells in columns and features in rows. Alternatively, a SummarizedExperiment object containing such a matrix.
`...` | For the generic, further arguments to pass to specific methods. For the SummarizedExperiment and SingleCellExperiment methods, further arguments to pass to the ANY method.
`subsets` | A named list containing one or more vectors (a character vector of cell names, a logical vector, or a numeric vector of indices), used to identify interesting sample subsets such as negative control wells.
`detection_limit` | A numeric scalar specifying the lower detection_limit for expression.
`BPPARAM` | A BiocParallelParam object specifying whether the QC calculations should be parallelized.
`flatten` | Logical scalar indicating whether the nested DataFrames in the output should be flattened.
`exprs_values` | A string or integer scalar indicating which `assays` in the `x` contains the count matrix.

### Details

This function calculates useful QC metrics for features, including the mean across all cells and the number of expressed features (i.e., counts above the detection_limit).

If `subsets` is specified, the same statistics are computed for each subset of cells. This is useful for obtaining statistics for cell sets of interest, e.g., negative control wells. These statistics are stored as nested DataFrames in the output. For example, if `subsets` contained `"empty"` and `"cellpool"`, the output would look like:

      output
      |-- mean
      |-- detected
      +-- subsets
          |-- empty
          |   |-- mean
          |   |-- detected
          |   +-- ratio
          +-- cellpool
              |-- mean
              |-- detected
              +-- ratio

The `ratio` field contains the ratio of the mean within each subset to the mean across all cells.

If `flatten=TRUE`, the nested DataFrames are flattened by concatenating the column names with underscores. This means that, say, the `subsets$empty$mean` nested field becomes the top-level `subsets_empty_mean` field. A flattened structure is more convenient for end-users performing interactive analyses, but less convenient for programmatic access as artificial construction of strings is required.

### Value

A DataFrame of QC statistics where each row corresponds to a row in `x`. This contains the following fields:

- `mean`: numeric, the mean counts for each feature.

- `detected`: numeric, the percentage of observations above `detection_limit`.

If `flatten=FALSE`, the output DataFrame also contains the `subsets` field. This a nested DataFrame containing per-feature QC statistics for each subset of columns.

If `flatten=TRUE`, `subsets` is flattened to remove the hierarchical structure.

### Author(s)

Aaron Lun

### See Also

`addPerFeatureQC`, to add the QC metrics to the row metadata.

### Examples

    example_sce <- mockSCE()
    stats <- perFeatureQCMetrics(example_sce)
    stats

    # With subsets.
    stats2 <- perFeatureQCMetrics(example_sce, subsets=list(Empty=1:10))
    stats2

[Package scater version 1.16.2 Index]