ExperimentSubset: Manages subsets of data with Bioconductor Experiment objects
27 October 2020
Package
ExperimentSubset 1.0.0
Contents
- 1 Installation
- 2 Motivation
- 3 A Brief Description
- 4 Overview of the
ExperimentSubsetclass - 5 Core methods of
ExperimentSubsetclass - 6 Using the
ExperimentSubsetobject: A toy example - 7 Using the
ExperimentSubsetobject: An example with real single cell RNA-seq data - 8 Methods for
ExperimentSubset - 9 Implementation Details
- 10 Session Information
1 Installation
if (!requireNamespace("BiocManager", quietly=TRUE)){
install.packages("BiocManager")}
BiocManager::install("ExperimentSubset")To install the latest version from Github, use the following code:
library(devtools)
install_github("campbio/ExperimentSubset")Loading the package:
library(ExperimentSubset)2 Motivation
Experiment objects such as the SummarizedExperiment or SingleCellExperiment
are data containers for one or more matrix-like assays along with the associated
row and column data. Often only a subset of the original data is needed for
down-stream analysis. For example, filtering out poor quality samples will
require excluding some columns before analysis. The ExperimentSubset object
is a container to efficiently manage different subsets of the same data without
having to make separate objects for each new subset.
3 A Brief Description
ExperimentSubset package enables users to perform flexible subsetting of
Single-Cell data that comes from the same experiment as well as the consequent
storage of these subsets back into the same object. In general, it offers the
same interface to the users as the SingleCellExperiment container which is
one the most widely used containers for Single-Cell data. However, in addition
to the features offered by SingleCellExperiment container, ExperimentSubset
offers subsetting features while hiding the implementation details from the
users. It does so by creating references to the subset rows and columns
instead of storing a new assay whenever possible. Functions from
SingleCellExperiment such as assay, rowData and colData can be used for
regular assays as one would normally do, as well as with newly created subsets
of the data. This allows the users to use the ExperimentSubset container
simply as if they were using SingleCellExperiment container with no change
required to the existing code.
4 Overview of the ExperimentSubset class
The ExperimentSubset class contains two slots, the root slot and the
subsets slot. The root slot is always an experiment object inherited from
SummarizedExperiment class, while the subsets slot is a list of subsets
created from the root object.
Each subset inside the ExperimentSubset object (more specifically inside the
subsets slot of the object) is stored as an AssaySubset instance. This
AssaySubset instance creates reference to the row and column indices for this
particular subset against a parent (which can either be the root object or
another subset). In case a new assay is to be stored against a subset, it is
stored as a separate experiment object (same class as the root) inside the
subset.
5 Core methods of ExperimentSubset class
While all the common methods available with SummarizedExperiment and
SingleCellExperiment classes have been overridden to support the
ExperimentSubset class with additional support for subsets, some core methods
for the creation and manipulation of subsets have been provided with the
ExperimentSubset class.
5.1 ExperimentSubset constructor
The constructor method allows the creation of an ExperimentSubset object from
an input experiment object as long as it is inherited from
SummarizedExperiment class. Additionally, if needed, a subset can be directly
created from within the constructor by providing input a named list to the
subset parameter.
counts <- matrix(rpois(100, lambda = 10), ncol=10, nrow=10)
sce <- SingleCellExperiment(list(counts = counts))
es <- ExperimentSubset(sce)
es## class: ExperimentSubset
## root class: SingleCellExperiment
## dim: 10 10
## metadata(0):
## assays(1): counts
## rownames: NULL
## rowData names(0):
## colnames: NULL
## colData names(0):
## reducedDimNames(0):
## altExpNames(0):
## subsets(0):
## subsetAssays(0):5.2 createSubset
The createSubset method as evident from the name, creates a subset from an
already available assay in the object. The subsetName (a character string),
rowIndices (a numeric or character vector), colIndices (a numeric or
character vector) and parentAssay (a character string) are the standard
parameters of the createSubset method. If rowIndices or colIndices are
missing or NULL, all of the rows or columns are selected from the specified
parentAssay. If parentAssay is missing or NULL, the first available
assay from the root object is linked as the parent of this subset. The
parentAssay can be an assay in the root object, a subset or an assay
within a subset.
The method accepts an ExperimentSubset object or any object inherited
from SummarizedExperiment for immediate conversion and the creation of the
subset through a single function call.
es <- createSubset(es,
subsetName = "subset1",
rows = c(1:2),
cols = c(1:5),
parentAssay = "counts")
es## class: ExperimentSubset
## root class: SingleCellExperiment
## dim: 10 10
## metadata(0):
## assays(1): counts
## rownames: NULL
## rowData names(0):
## colnames: NULL
## colData names(0):
## reducedDimNames(0):
## altExpNames(0):
## subsets(1): subset1
## subsetAssays(1): subset15.3 storeSubset
The storeSubset method should be used when a subset assay needs to be stored
either in a previously created subset or a new subset. This is specifically
different from the createSubset method which only creates a subset by
referencing to a defined parentAssay where the internalAssay of the subset
has no assays stored. The storeSubset method however, is used to store an
assay in this internalAssay slot of the subset which in fact is a subset
experiment object of the same class as the root object. Additionally, the
storeSubset method can be used to directly create a subset and then store an
assay inside this subset depending upon the parameters with which the method
is called.
subset1Assay <- assay(es, "subset1")
subset1Assay[,] <- subset1Assay[,] + 1
es <- storeSubset(es,
subsetName = "subset1",
inputMatrix = subset1Assay,
subsetAssayName = "subset1Assay")
es## class: ExperimentSubset
## root class: SingleCellExperiment
## dim: 10 10
## metadata(0):
## assays(1): counts
## rownames: NULL
## rowData names(0):
## colnames: NULL
## colData names(0):
## reducedDimNames(0):
## altExpNames(0):
## subsets(1): subset1
## subsetAssays(2): subset1 subset1AssayThe parameters of interest against this method are subsetName which specifies
the name of the subset inside which the an input assay should be stored,
inputMatrix which is a matrix-type object to be stored as an assay inside a
subset specified by the subsetName parameter and lastly the subsetAssayName
parameter which represents the name of the new assay. If subsetAssayName is
set to NULL, a new subset is created and the inputMatrix is stored inside
the new subset.
5.4 subsetSummary
The subsetSummary method displays an overall summary of the
ExperimentSubset object including the assays in the root object, the list
of subsets along with the stored assays, reduced dimensions, alt experiments
and other supplementary information that may help the users understand the
current condition of the object. The most important piece of information
displayed by this method is the hierarchical parent-subset link against each
subset in the object.
subsetSummary(es)## Main assay(s):
## counts
##
## Subset(s):
## Name Dim Parent Assays
## 1 subset1 2, 5 counts subset1Assay5.5 Additional helper methods
Some additional helper methods are available for the users to use during
certain circumstances such as during iteration of all subsets. These methods
include subsetNames that returns a character vector of all available
subsets, subsetAssayNames that returns a character vector of all available
subsets and the assays within these subsets, subsetCount that returns the
count of the subsets, subsetAssayCount that returns the total count of the sum
of the subsets and the assays within these subsets, subsetDim that returns the
dimensions of a subset and lastly the subsetParent method that returns a
character list of complete parent hierarchy of a subset.
5.6 Overriden methods for ExperimentSubset class
These are the methods that have been overridden from other classes to support
the subset feature of the ExperimentSubset objects by introducing an
additional parameter subsetName to these methods. These methods can simply
be called on any ExperimentSubset object to get or set from the root object
or from any subset by passing the optional subsetName parameter.
The methods include assay, assay<-, rowData, rowData<-, colData,
colData<-, metadata, metadata<-, reducedDim, reducedDim<-,
reducedDims, reducedDims<-, reducedDimNames, reducedDimNames<-,
altExp, altExp<-, altExps, altExps<-, altExpNames, altExpNames<-,
rownames, rownames<-, colnames and colnames<-. All of the methods
can be used with the subsets by providing the optional subsetName parameter.
6 Using the ExperimentSubset object: A toy example
Creating the ExperimentSubset object is as simple as passing an experiment
object to the ExperimentSubset constructor:
counts <- matrix(rpois(100, lambda = 10), ncol=10, nrow=10)
sce <- SingleCellExperiment(list(counts = counts))
es <- ExperimentSubset(sce)
subsetSummary(es)## Main assay(s):
## counts
##
## Subset(s):
## NULLCreate a subset that includes the first 5 rows and columns only:
es <- createSubset(es,
subsetName = "subset1",
rows = c(1:5),
cols = c(1:5),
parentAssay = "counts")
subsetSummary(es)## Main assay(s):
## counts
##
## Subset(s):
## Name Dim Parent
## 1 subset1 5, 5 countsCreate another subset from subset1 by only keeping the first two rows:
es <- createSubset(es,
subsetName = "subset2",
rows = c(1:2),
cols = c(1:5),
parentAssay = "subset1")
subsetSummary(es)## Main assay(s):
## counts
##
## Subset(s):
## Name Dim Parent
## 1 subset1 5, 5 counts
## 2 subset2 2, 5 subset1 -> countsGet assay from subset2 and update values:
subset2Assay <- assay(es, "subset2")
subset2Assay[,] <- subset2Assay[,] + 1Store the updated assay back to subset2 using one of the two approaches:
#approach 1
es <- storeSubset(es,
subsetName = "subset2",
inputMatrix = subset2Assay,
subsetAssayName = "subset2Assay_a1")
#approach 2
assay(es, "subset2", subsetAssayName = "subset2Assay_a2") <- subset2Assay
subsetSummary(es)## Main assay(s):
## counts
##
## Subset(s):
## Name Dim Parent Assays
## 1 subset1 5, 5 counts
## 2 subset2 2, 5 subset1 -> counts c("subset2Assay_a1", "subset2Assay_a2")Store an experiment object in the altExp slot of subset2:
altExp(x = es,
e = "subset2_alt1",
subsetName = "subset2") <- SingleCellExperiment(assay = list(
counts = assay(es, "subset2")
))Show the current condition of ExperimentSubset object:
subsetSummary(es)## Main assay(s):
## counts
##
## Subset(s):
## Name Dim Parent Assays
## 1 subset1 5, 5 counts
## 2 subset2 2, 5 subset1 -> counts c("subset2Assay_a1", "subset2Assay_a2")
## AltExperiments
## 1
## 2 subset2_alt17 Using the ExperimentSubset object: An example with real single cell RNA-seq data
Installing and loading required packages:
if (!requireNamespace("BiocManager", quietly = TRUE))
install.packages("BiocManager")
BiocManager::install(version = "3.11", ask = FALSE)
BiocManager::install(c("TENxPBMCData", "scater", "scran"))library(ExperimentSubset)
library(TENxPBMCData)
library(scater)
library(scran)Load PBMC4K dataset and create ExperimentSubset object:
tenx_pbmc4k <- TENxPBMCData(dataset = "pbmc4k")
es <- ExperimentSubset(tenx_pbmc4k)
subsetSummary(es)Compute perCellQCMetrics on counts matrix:
perCellQCMetrics <- perCellQCMetrics(assay(es, "counts"))
colData(es) <- cbind(colData(es), perCellQCMetrics)Filter cells with low column sum and create a new subset called ‘filteredCells’:
filteredCellsIndices <- which(colData(es)$sum > 1500)
es <- createSubset(es, "filteredCells", cols = filteredCellsIndices, parentAssay = "counts")
subsetSummary(es)Normalize ‘filteredCells’ subset using scater library and store it back:
assay(es, "filteredCells", subsetAssayName = "filteredCellsNormalized") <- normalizeCounts(assay(es, "filteredCells"))
subsetSummary(es)Find highly variable genes from the normalized assay in the previous step using scran library against the ‘filteredCells’ subset only:
topHVG1000 <- getTopHVGs(modelGeneVar(assay(es, "filteredCellsNormalized")), n = 1000)
es <- createSubset(es, "hvg1000", rows = topHVG1000, parentAssay = "filteredCellsNormalized")
subsetSummary(es)Run ‘PCA’ on the highly variable genes computed in the last step using scater library against the ‘filteredCells’ subset only:
reducedDim(es, type = "PCA", subsetName = "hvg1000") <- calculatePCA(assay(es, "hvg1000"))Show the current condition of the ExperimentSubset object:
subsetSummary(es)8 Methods for ExperimentSubset
ExperimentSubsetconstructorcreateSubsetstoreSubsetsubsetSummarysubsetParentsubsetCountsubsetAssayCountsubsetNamessubsetAssayNamessubsetDimsubsetRowDatasubsetColDatashowassayassay<-rowDatarowData<-colDatacolData<-metadatametadata<-reducedDimreducedDim<-reducedDimsreducedDims<-reducedDimNamesreducedDimNames<-,altExpaltExp<-altExpsaltExps<-altExpNamesaltExpNames<-rownamesrownames<-colnamescolnames<-
9 Implementation Details
The internal structure of an ExperimentSubset class is described
below:
9.1 root slot
The root slot of an ExperimentSubset object must be an experiment object
inherited from SummarizedExperiment or SingleCellExperiment and acts as the
root or the first immediate parent of any subset that is created initially. The
ExperimentSubsetobject can be used in a fashion similar to
SummarizedExperiment with all the common methods that have been overridden to
support the manipulation of ExperimentSubset objects (with or without subsets)
including assay, rowData and colData. Even though all of these methods
can be used with either ExperimentSubset or other experiment objects directly,
the accessible root slot offers a convenient way to manipulate the original
object if required by the user.
9.2 subsets slot
The subsets slot of the ExperimentSubset object is a list, where each
element in this list is an object of an internal AssaySubset class. Each
element represents one subset linked to the experiment object in the root
slot. The structure of each subset is described below:
9.2.1 subsetName
A character string that represents a user-defined name of the subset.
9.2.2 rowIndices
A numeric vector that stores the indices of the selected rows in the linked
parent assay within for this subset.
9.2.3 colIndices
A numeric vector that stores the indices of the selected columns in the
linked parent assay for this subset.
9.2.4 parentAssay
A character string that stores the name of the immediate parent to which the
subset is linked. The parentAssay can be an assay in the root slot of the
ExperimentSubset object or any subset or any internalAssay of a subset.
9.2.5 internalAssay
The internalAssay slot stores an experiment object of same type as the root
object but with the dimensions of the subset. The internalAssay is initially
an empty experiment object with only dimensions set to enable manipulation, but
can be used to store additional data against a subset such as assay,
rowData, colData, reducedDims, altExps and metadata.
10 Session Information
sessionInfo()## R version 4.0.3 (2020-10-10)
## Platform: x86_64-w64-mingw32/x64 (64-bit)
## Running under: Windows Server 2012 R2 x64 (build 9600)
##
## Matrix products: default
##
## locale:
## [1] LC_COLLATE=C
## [2] LC_CTYPE=English_United States.1252
## [3] LC_MONETARY=English_United States.1252
## [4] LC_NUMERIC=C
## [5] LC_TIME=English_United States.1252
##
## attached base packages:
## [1] parallel stats4 stats graphics grDevices utils datasets
## [8] methods base
##
## other attached packages:
## [1] ExperimentSubset_1.0.0 SingleCellExperiment_1.12.0
## [3] SummarizedExperiment_1.20.0 Biobase_2.50.0
## [5] GenomicRanges_1.42.0 GenomeInfoDb_1.26.0
## [7] IRanges_2.24.0 S4Vectors_0.28.0
## [9] BiocGenerics_0.36.0 MatrixGenerics_1.2.0
## [11] matrixStats_0.57.0 BiocStyle_2.18.0
##
## loaded via a namespace (and not attached):
## [1] knitr_1.30 XVector_0.30.0 magrittr_1.5
## [4] zlibbioc_1.36.0 lattice_0.20-41 rlang_0.4.8
## [7] stringr_1.4.0 tools_4.0.3 grid_4.0.3
## [10] xfun_0.18 htmltools_0.5.0 yaml_2.2.1
## [13] digest_0.6.27 bookdown_0.21 Matrix_1.2-18
## [16] GenomeInfoDbData_1.2.4 BiocManager_1.30.10 bitops_1.0-6
## [19] RCurl_1.98-1.2 evaluate_0.14 rmarkdown_2.5
## [22] DelayedArray_0.16.0 stringi_1.5.3 compiler_4.0.3