A description of the PipelineDefinition for scRNAseq clustering and its evaluation metrics.
pipeComp 1.16.0
This vignette is centered around the application of pipeComp to scRNA-seq clustering pipelines, and assumes a general understanding of pipeComp (for an overview, see the pipeComp vignette).
The scRNAseq PipelineDefinition
comes in two variants determined by the object used as a backbone, either SingleCellExperiment (SCE) or seurat (see ?scrna_pipeline
). Both use the same evaluation metrics, and most method wrappers included in the package have been made so that they are compatible with both. For simplicity, we will therefore stick to just one variant here, and will focus on few very basic comparisons to illustrate the main functionalities, metrics and evaluation plots. For more detailed benchmarks, refer to our preprint:
pipeComp, a general framework for the evaluation of computational pipelines, reveals performant single-cell RNA-seq preprocessing tools
Pierre-Luc Germain, Anthony Sonrel & Mark D Robinson,
bioRxiv 2020.02.02.930578
The PipelineDefinition
can be obtained with the following function:
library(pipeComp)
# we use the variant of the pipeline used in the paper
pipDef <- scrna_pipeline(pipeClass = "seurat")
pipDef
## A PipelineDefinition object with the following steps:
## - doublet(x, doubletmethod) *
## Takes a SCE object with the `phenoid` colData column, passes it through the
## function `doubletmethod`, and outputs a filtered SCE.
## - filtering(x, filt) *
## Takes a SCE object, passes it through the function `filt`, and outputs a
## filtered Seurat object.
## - normalization(x, norm) *
## Passes the object through function `norm` and returns it with the normalized and scale data slots filled.
## - selection(x, sel, selnb=2000)
## Returns a Seurat object with the VariableFeatures filled with `selnb` features
## using the function `sel`.
## - dimreduction(x, dr, maxdim=50) *
## Returns a Seurat object with the PCA reduction with up to `maxdim` components
## using the `dr` function.
## - clustering(x, clustmethod, dims=20, k=20, steps=8, resolution=c(0.01, 0.1, 0.5, 0.8, 1), min.size=50) *
## Uses function `clustmethod` to return a named vector of cell clusters.
To illustrate the use of the pipeline, we will run a basic comparison using wrappers that are included in the package. However, in order for pipeComp not to systematically require the installation of all dependencies related to all methods for which there are wrappers, they were not included in the package code but rather as source files, which can be loaded in the following way:
source(system.file("extdata", "scrna_alternatives.R", package="pipeComp"))
(To know which packages are required by the set of wrappers you intend to use, see ?checkPipelinePackages
)
Any function that has been loaded in the environment can then be used as alternative. We define a small set of alternatives to test:
alternatives <- list(
doubletmethod=c("none"),
filt=c("filt.lenient", "filt.stringent"),
norm=c("norm.seurat", "norm.sctransform", "norm.scran"),
sel=c("sel.vst"),
selnb=2000,
dr=c("seurat.pca"),
clustmethod=c("clust.seurat"),
dims=c(10, 15, 20, 30),
resolution=c(0.01, 0.1, 0.2, 0.3, 0.5, 0.8, 1, 1.2, 2)
)
We also assume three datasets in (SCE) format (not included in the package - see the last section of this vignette) and run the pipeline:
# available on https://doi.org/10.6084/m9.figshare.11787210.v1
datasets <- c( mixology10x5cl="/path/to/mixology10x5cl.SCE.rds",
simMix2="/path/to/simMix2.SCE.rds",
Zhengmix8eq="/path/to/Zhengmix8eq.SCE.rds" )
# not run
res <- runPipeline( datasets, alternatives, pipDef, nthreads=3)
Instead of running the analyses here, we will load the final example results:
data("exampleResults", package = "pipeComp")
res <- exampleResults
Benchmark metrics are organized according to the step at which they are computed, and will be presented here in this fashion. This does not mean that they are relevant only for that step: alternative parameters at a given step can also be evaluated with respect to the metrics defined in all downstream steps.
The evaluation performed after the first two steps (doublet detection and filtering) is the same:
head(res$evaluation$filtering)
## dataset doubletmethod filt subpopulation N.before N.lost
## 1 mixology10x5cl none filt.lenient A549 1244 0
## 2 mixology10x5cl none filt.lenient H1975 515 1
## 3 mixology10x5cl none filt.lenient H2228 751 0
## 4 mixology10x5cl none filt.lenient H838 840 0
## 5 mixology10x5cl none filt.lenient HCC827 568 0
## 6 mixology10x5cl none filt.stringent A549 1244 40
## pc.lost
## 1 0.000
## 2 0.194
## 3 0.000
## 4 0.000
## 5 0.000
## 6 3.215
For each method and subpopulation, we report:
N.before
the number of cells before the stepN.lost
the number of cells excluded by the steppc.lost
the percentage of cells lost (relative to the supopulation)As noted in our manuscript, stringent filtering can lead to strong bias against certain supopulations. We therefore especially monitor the max pc.lost
of different methods in relation to the impact on clustering accuracy (privileging, at this step, metrics that are not dependent on the relative abundances of the subpopulations, such as the mean F1 score per subpopulation). This can conveniently be done using the following function:
scrna_evalPlot_filtering(res)
Evaluations based on the reduced space are much more varied:
names(res$evaluation$dimreduction)
## [1] "silhouette" "varExpl.subpops" "corr.covariate"
## [4] "meanAbsCorr.covariate2" "PC1.covar.adjR2"
The silhouette
slot contains information about the silhouettes width of true subpopulations. Depending on the methods used for dimensionality (i.e. fixed vs estimated number of dimensions), there will be a single output or outputs for different sets of dimensions, as it is the case in our example:
names(res$evaluation$dimreduction$silhouette)
## [1] "top_10_dims" "top_20_dims" "all_50_dims"
For each of them we have a data.frame including, for each subpopulation in each analysis (i.e. combination of parameters), the minimum, maximum, median and mean silhouette width:
head(res$evaluation$dimreduction$silhouette$top_10_dims)
## dataset doubletmethod filt norm sel selnb
## 1 mixology10x5cl none filt.lenient norm.seurat sel.vst 2000
## 2 mixology10x5cl none filt.lenient norm.seurat sel.vst 2000
## 3 mixology10x5cl none filt.lenient norm.seurat sel.vst 2000
## 4 mixology10x5cl none filt.lenient norm.seurat sel.vst 2000
## 5 mixology10x5cl none filt.lenient norm.seurat sel.vst 2000
## 6 mixology10x5cl none filt.lenient norm.sctransform sel.vst 2000
## dr maxdim subpopulation minSilWidth meanSilWidth medianSilWidth
## 1 seurat.pca 50 A549 0.3723309 0.6396069 0.6516611
## 2 seurat.pca 50 H1975 -0.6114923 0.1949538 0.2873076
## 3 seurat.pca 50 H2228 -0.1413490 0.4832060 0.4954937
## 4 seurat.pca 50 H838 0.3459593 0.5961926 0.6059980
## 5 seurat.pca 50 HCC827 0.2384042 0.5800197 0.5967093
## 6 seurat.pca 50 A549 0.1339476 0.6333684 0.6518073
## maxSilWidth
## 1 0.7367229
## 2 0.4217019
## 3 0.6130284
## 4 0.7056178
## 5 0.6876504
## 6 0.7326905
This information can be plotted using the function scrna_evalPlot_silh
; the function outputs a ComplexHeatmap, which means that many arguments of that package and options can be used, for instance:
library(ComplexHeatmap)
## Loading required package: grid
## ========================================
## ComplexHeatmap version 2.22.0
## Bioconductor page: http://bioconductor.org/packages/ComplexHeatmap/
## Github page: https://github.com/jokergoo/ComplexHeatmap
## Documentation: http://jokergoo.github.io/ComplexHeatmap-reference
##
## If you use it in published research, please cite either one:
## - Gu, Z. Complex Heatmap Visualization. iMeta 2022.
## - Gu, Z. Complex heatmaps reveal patterns and correlations in multidimensional
## genomic data. Bioinformatics 2016.
##
##
## The new InteractiveComplexHeatmap package can directly export static
## complex heatmaps into an interactive Shiny app with zero effort. Have a try!
##
## This message can be suppressed by:
## suppressPackageStartupMessages(library(ComplexHeatmap))
## ========================================
scrna_evalPlot_silh( res )
h <- scrna_evalPlot_silh( res, heatmap_legend_param=list(direction="horizontal") )
draw(h, heatmap_legend_side="bottom", annotation_legend_side = "bottom", merge_legend=TRUE)
See ?scrna_evalPlot_silh
for more options.
The slot varExpl.subpops
indicates, for each analysis, the proportion of variance of each principal component explained by the true supopulations.
res$evaluation$dimreduction$varExpl.subpops[1:5,1:15]
## dataset doubletmethod filt norm sel selnb
## 1 mixology10x5cl none filt.lenient norm.seurat sel.vst 2000
## 2 mixology10x5cl none filt.lenient norm.sctransform sel.vst 2000
## 3 mixology10x5cl none filt.lenient norm.scran sel.vst 2000
## 4 mixology10x5cl none filt.stringent norm.seurat sel.vst 2000
## 5 mixology10x5cl none filt.stringent norm.sctransform sel.vst 2000
## dr maxdim PC_1 PC_10 PC_11 PC_12 PC_13
## 1 seurat.pca 50 0.9631018 0.007716938 0.001831543 0.0015462150 0.0022304080
## 2 seurat.pca 50 0.9511425 0.007395324 0.002717310 0.0006250593 0.0118729485
## 3 seurat.pca 50 0.2369999 0.005925415 0.009554253 0.0055803311 0.0002206834
## 4 seurat.pca 50 0.9643754 0.007433402 0.002014857 0.0017917112 0.0026884483
## 5 seurat.pca 50 0.9586863 0.008118786 0.003153175 0.0005636794 0.0124421034
## PC_14 PC_15
## 1 0.0007939924 0.002998006
## 2 0.0044840040 0.004285101
## 3 0.0006480071 0.000983346
## 4 0.0008178260 0.003457408
## 5 0.0033090652 0.003800675
The following slots in res$evaluation$dimreduction
track the correlation between principal components (PCs) and predefined cell-level covariates such as library size and number of detected genes:
* corr.covariate
contains the pearson correlation between the covariates and each PC; however, since there are major differences in library sizes between subpopulations, we advise against using this directly.
* meanAbsCorr.covariate2
circumvents this bias by computing the mean absolute correlation (among the first 5 components) for each subpopulation, and averaging them.
* PC1.covar.adjR2
gives the difference in adjusted R^2 between a model fit on PC1 containing the covariate along with subpopulations (PC1~subpopulation+covariate) and one without the covariate (PC1~subpopulation).
These metrics, as well as the following ones, can be plotted using generic pipeComp
plotting functions, for example:
evalHeatmap(res, step="dimreduction", what="log10_total_features",
what2="meanAbsCorr.covariate2")