ExperimentSubset: Manages subsets of data with Bioconductor Experiment objects
Installation
if (!requireNamespace("BiocManager", quietly=TRUE)){
install.packages("BiocManager")}
BiocManager::install("ExperimentSubset")To install the latest version from Github, use the following code:
Loading the package:
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 and can be
used as a drop-in replacement for other experiment classes.
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 instead of actually
copying the redundant data. 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.
Overview of the ExperimentSubset class
The ExperimentSubset package is composed of multiple
classes that support subsets management capability depending upon the
class of the input experiment object. The currently supported experiment
classes which can be used with ExperimentSubset include
SummarizedExperiment,
RangedSummarizedExperiment and
SingleCellExperiment.
The ExperimentSubset package adds an additional slot
subsets to the objects from these classes which enables
support for the creation and management of subsets of data.
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 be
the inherited parent 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 inherited object) inside the subset.
Core methods of ExperimentSubset class
While all 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.
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: SubsetSingleCellExperiment
## dim: 10 10
## metadata(0):
## assays(1): counts
## rownames: NULL
## rowData names(0):
## colnames: NULL
## colData names(0):
## reducedDimNames(0):
## mainExpName: NULL
## altExpNames(0):
## subsets(0):
## subsetAssays(0):Additionally, an ExperimentSubset object can also be
created directly from generally loaded data such as counts matrices,
which can be passed to the constructor function in a list.
## class: SubsetSingleCellExperiment
## dim: 10 10
## metadata(0):
## assays(1): counts
## rownames: NULL
## rowData names(0):
## colnames: NULL
## colData names(0):
## reducedDimNames(0):
## mainExpName: NULL
## altExpNames(0):
## subsets(0):
## subsetAssays(0):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 parent object is linked as the parent
of this subset. The parentAssay can be an
assay in the parent object, a subset or an
assay within a subset.
es <- createSubset(es,
subsetName = "subset1",
rows = c(1:2),
cols = c(1:5),
parentAssay = "counts")
es## class: SubsetSingleCellExperiment
## dim: 10 10
## metadata(0):
## assays(1): counts
## rownames: NULL
## rowData names(0):
## colnames: NULL
## colData names(0):
## reducedDimNames(0):
## mainExpName: NULL
## altExpNames(0):
## subsets(1): subset1
## subsetAssays(1): subset1setSubsetAssay and getSubsetAssay
The setSubsetAssay method should be used when a subset
assay needs to be stored either in a previously created
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
setSubsetAssay 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
parent object.
subset1Assay <- assay(es, "subset1")
subset1Assay[,] <- subset1Assay[,] + 1
es <- setSubsetAssay(es,
subsetName = "subset1",
inputMatrix = subset1Assay,
subsetAssayName = "subset1Assay")
es## class: SubsetSingleCellExperiment
## dim: 10 10
## metadata(0):
## assays(1): counts
## rownames: NULL
## rowData names(0):
## colnames: NULL
## colData names(0):
## reducedDimNames(0):
## mainExpName: NULL
## 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.
To get a subset assay, getSubsetAssay method can be
used:
## [,1] [,2] [,3] [,4] [,5]
## [1,] 11 13 8 10 12
## [2,] 6 7 8 13 11## [,1] [,2] [,3] [,4] [,5]
## [1,] 12 14 9 11 13
## [2,] 7 8 9 14 12Apart from setSubsetAssay and
getSubsetAssay methods, assay and
assay<- methods can also be used for the same purpose.
Their usage has been described in the overridden methods section
below.
subsetSummary
The subsetSummary method displays an overall summary of
the ExperimentSubset object including the assays in the
parent 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.
## Main assay(s):
## counts
##
## Subset(s):
## Name Dim Parent Assays
## 1 subset1 2, 5 counts subset1AssayAdditional helper methods
Helper methods have been provided for use by the users during specific circumstances while manipulating subsets of data. These helper methods and their short descriptions are given below:
subsetNamesReturns the names of all available subsets (excluding internal subset assays)subsetAssayNamesReturns the names of all available subsets (including internal subset assays)subsetCountReturns the total count of the subsets (excluding internal subset assays)subsetAssayCountReturns the total count of the subsets (including internal subset assays)subsetDimReturns the dimensions of a specified subsetsubsetColDataGets or sets colData from/to a subsetsubsetRowDataGets or sets rowData from/to a subsetsubsetColnamesGets or sets colnames from/to a subsetsubsetRownamesGets or sets rownames from/to a subsetsubsetParentReturns the ’subset-parent` link of a specified subsetsetSubsetAssaySets an assay to a subsetgetSubsetAssayGets an assay from a subset
subsetColData & subsetRowData
Both subsetColData and subsetrowData getter
methods take in an additional logical parameter
parentColData or parentRowData that specifies
if the returned ‘colData’ or ‘rowData’ should include the ‘colData’ and
‘rowData’ from the parent object as well. By default,
parentColData and parentRowData parameters are
set to FALSE. Same applies to the usage of inherited
rowData and colData methods.
#store colData to parent object
colData(es) <- cbind(colData(es), sampleID = seq(1:dim(es)[2]))
#store colData to 'subset1' using option 1
colData(es, subsetName = "subset1") <- cbind(
colData(es, subsetName = "subset1"),
subsetSampleID1 = seq(1:subsetDim(es, "subset1")[2]))
#store colData to 'subset1' using option 2
subsetColData(es, "subset1") <- cbind(
subsetColData(es, "subset1"),
subsetSampleID2 = seq(1:subsetDim(es, "subset1")[2]))
#get colData from 'subset1' without parent colData
subsetColData(es, "subset1", parentColData = FALSE)## DataFrame with 5 rows and 2 columns
## subsetSampleID1 subsetSampleID2
## <integer> <integer>
## 1 1 1
## 2 2 2
## 3 3 3
## 4 4 4
## 5 5 5## DataFrame with 5 rows and 3 columns
## sampleID subsetSampleID1 subsetSampleID2
## <integer> <integer> <integer>
## 1 1 1 1
## 2 2 2 2
## 3 3 3 3
## 4 4 4 4
## 5 5 5 5#same applies to `colData` and `rowData` methods when using with subsets
colData(es, subsetName = "subset1", parentColData = FALSE) #without parent data## DataFrame with 5 rows and 2 columns
## subsetSampleID1 subsetSampleID2
## <integer> <integer>
## 1 1 1
## 2 2 2
## 3 3 3
## 4 4 4
## 5 5 5## DataFrame with 5 rows and 3 columns
## sampleID subsetSampleID1 subsetSampleID2
## <integer> <integer> <integer>
## 1 1 1 1
## 2 2 2 2
## 3 3 3 3
## 4 4 4 4
## 5 5 5 5Overridden 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 parent
object or from any subset by passing the optional
subsetName parameter.
The methods include rowData, rowData<-,
colData, colData<-, metadata,
metadata<-, reducedDim,
reducedDim<-, reducedDims,
reducedDims<-, reducedDimNames,
reducedDimNames<-, altExp,
altExp<-, altExps,
altExps<-, altExpNames and
altExpNames<-. All of the methods can be used with the
subsets by providing the optional subsetName parameter.
assay-get & assay-set inherited methods
An exception to the above approach is the use of assay
and assay<- methods, both of which have a slightly
different usage as described below:
Because the assay<- setter method in the case of a
subset needs to store the assay inside the subset, we need to specify
the subset name inside which the assay should be stored as
i parameter and define the new name of the subset assay as
the additional subsetAssayName parameter.
#creating a dummy ES object
counts <- matrix(rpois(100, lambda = 10), ncol=10, nrow=10)
sce <- SingleCellExperiment(list(counts = counts))
es <- ExperimentSubset(sce)
#create a subset
es <- createSubset(es, subsetName = "subset1", rows = c(1:2), cols = c(1:4))
#store an assay inside the newly created 'subset1'
#note that 'assay<-' setter has two important parameters 'x' and 'i' where
#'x' is the object and 'i' is the assay name, but in the case of storing to a
#subset we use 'x' as the object, 'i' as the subset name inside which the assay
#should be stored and an additional 'subsetAssayName' parameter which defines
#the name of the new assay
assay(
x = es,
i = "subset1",
subsetAssayName = "subset1InternalAssay") <- matrix(rpois(100, lambda = 10),
ncol=4, nrow=2)Using assay getter method is simple, as no additional
parameter is required unlike in the setter method.
#assay getter has parameters 'x' which is the input object, 'i' which can either
#be a assay name in the parent object, a subset name or a subset assay name
#getting 'counts' from parent es object
assay(
x = es,
i = "counts"
)## [,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10]
## [1,] 11 16 12 6 8 8 11 13 7 15
## [2,] 6 8 6 8 16 8 6 8 9 9
## [3,] 6 6 13 12 12 12 14 5 13 5
## [4,] 13 10 9 11 5 14 5 13 11 6
## [5,] 9 8 16 5 8 4 14 8 6 6
## [6,] 13 7 8 11 10 11 5 5 16 13
## [7,] 11 12 7 9 12 13 16 10 7 8
## [8,] 8 10 13 14 11 10 14 8 7 12
## [9,] 9 17 14 10 8 15 9 4 13 8
## [10,] 17 8 10 13 10 7 13 9 8 8## [,1] [,2] [,3] [,4]
## [1,] 11 16 12 6
## [2,] 6 8 6 8#getting the 'subset1InternalAssay' from inside the 'subset1'
assay(
x = es,
i = "subset1InternalAssay"
)## [,1] [,2] [,3] [,4]
## [1,] 10 10 8 11
## [2,] 17 11 8 9Using 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:
Store the updated assay back to subset2
using one of the two approaches:
#approach 1
es <- setSubsetAssay(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 subset2Assay_a1, subset2Assay_a2Store 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:
## Main assay(s):
## counts
##
## Subset(s):
## Name Dim Parent Assays
## 1 subset1 5, 5 counts
## 2 subset2 2, 5 subset1 -> counts subset2Assay_a1, subset2Assay_a2
## AltExperiments
## 1
## 2 subset2_alt1Using 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"))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:
Show the current condition of the ExperimentSubset
object:
Supported Input Object Classes
- SummarizedExperiment
- RangedSummarizedExperiment
- SingleCellExperiment
- TreeSummarizedExperiment
- SpatialExperiment
Methods for ExperimentSubset
ExperimentSubsetconstructorcreateSubsetsetSubsetAssaygetSubsetAssaysubsetSummarysubsetParentsubsetCountsubsetAssayCountsubsetNamessubsetAssayNamessubsetDimsubsetRowDatasubsetColDatasubsetColnamessubsetRownamessubsetRowData<-subsetColData<-subsetColnames<-subsetRownames<-showassayassay<-rowDatarowData<-colDatacolData<-metadatametadata<-reducedDimreducedDim<-reducedDimsreducedDims<-reducedDimNamesreducedDimNames<-altExpaltExp<-altExpsaltExps<-altExpNamesaltExpNames<-subsetSpatialCoordssubsetSpatialDatasubsetSpatialData<-subsetRowLinkssubsetColLinksspatialCoordsspatialDataspatialData<-rowLinkscolLinks
Implementation Details
The internal structure of an ExperimentSubset class is
described below:
Inherited parent object
The ExperimentSubset object during creation is assigned
one of the classes from SubsetSummarizedExperiment,
SubsetRangedSummarizedExperiment or
SubsetSingleCellExperiment which inherit from the class of
the input object. This ensures that ExperimentSubset object
can be manipulated in a fashion similar to the input object class and so
can be used as a drop-in replacement for these classes. All methods that
are compatible with the input object class are compatible with the
ExperimentSubset objects as well.
Additional subsets slot
The subsets slot of the ExperimentSubset
object is a SimpleList, where each element in this list is
an object of an internal AssaySubset class. The slot itself
is not directly accessible to the users and should be accessed through
the provided methods of the ExperimentSubset package. Each
element represents one subset linked to the experiment object in the
parent object. The structure of each subset is described below:
subsetName
A character string that represents a user-defined name
of the subset.
rowIndices
A numeric vector that stores the indices of
the selected rows in the linked parent assay within for this subset.
colIndices
A numeric vector that stores the indices of
the selected columns in the linked parent assay for this subset.
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 parent ExperimentSubset
object or any subset or any internalAssay of a subset.
internalAssay
The internalAssay slot stores an experiment object of
same type as the input 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.
Session Information
## R version 4.4.1 (2024-06-14)
## Platform: x86_64-pc-linux-gnu
## Running under: Ubuntu 24.04.1 LTS
##
## Matrix products: default
## BLAS: /usr/lib/x86_64-linux-gnu/openblas-pthread/libblas.so.3
## LAPACK: /usr/lib/x86_64-linux-gnu/openblas-pthread/libopenblasp-r0.3.26.so; LAPACK version 3.12.0
##
## locale:
## [1] LC_CTYPE=en_US.UTF-8 LC_NUMERIC=C
## [3] LC_TIME=en_US.UTF-8 LC_COLLATE=C
## [5] LC_MONETARY=en_US.UTF-8 LC_MESSAGES=en_US.UTF-8
## [7] LC_PAPER=en_US.UTF-8 LC_NAME=C
## [9] LC_ADDRESS=C LC_TELEPHONE=C
## [11] LC_MEASUREMENT=en_US.UTF-8 LC_IDENTIFICATION=C
##
## time zone: Etc/UTC
## tzcode source: system (glibc)
##
## attached base packages:
## [1] stats4 stats graphics grDevices utils datasets methods
## [8] base
##
## other attached packages:
## [1] ExperimentSubset_1.17.0 TreeSummarizedExperiment_2.13.0
## [3] Biostrings_2.75.0 XVector_0.45.0
## [5] SpatialExperiment_1.15.1 SingleCellExperiment_1.27.2
## [7] SummarizedExperiment_1.35.5 Biobase_2.67.0
## [9] GenomicRanges_1.57.2 GenomeInfoDb_1.41.2
## [11] IRanges_2.39.2 S4Vectors_0.43.2
## [13] BiocGenerics_0.53.0 MatrixGenerics_1.17.1
## [15] matrixStats_1.4.1 BiocStyle_2.35.0
##
## loaded via a namespace (and not attached):
## [1] rjson_0.2.23 xfun_0.48 bslib_0.8.0
## [4] lattice_0.22-6 yulab.utils_0.1.7 vctrs_0.6.5
## [7] tools_4.4.1 generics_0.1.3 parallel_4.4.1
## [10] tibble_3.2.1 fansi_1.0.6 pkgconfig_2.0.3
## [13] Matrix_1.7-1 lifecycle_1.0.4 GenomeInfoDbData_1.2.13
## [16] compiler_4.4.1 treeio_1.29.2 codetools_0.2-20
## [19] htmltools_0.5.8.1 sys_3.4.3 buildtools_1.0.0
## [22] sass_0.4.9 lazyeval_0.2.2 yaml_2.3.10
## [25] tidyr_1.3.1 pillar_1.9.0 crayon_1.5.3
## [28] jquerylib_0.1.4 BiocParallel_1.41.0 DelayedArray_0.31.14
## [31] cachem_1.1.0 magick_2.8.5 abind_1.4-8
## [34] nlme_3.1-166 tidyselect_1.2.1 digest_0.6.37
## [37] purrr_1.0.2 dplyr_1.1.4 maketools_1.3.1
## [40] fastmap_1.2.0 grid_4.4.1 cli_3.6.3
## [43] SparseArray_1.5.45 magrittr_2.0.3 S4Arrays_1.5.11
## [46] utf8_1.2.4 ape_5.8 UCSC.utils_1.1.0
## [49] rmarkdown_2.28 httr_1.4.7 evaluate_1.0.1
## [52] knitr_1.48 rlang_1.1.4 Rcpp_1.0.13
## [55] tidytree_0.4.6 glue_1.8.0 BiocManager_1.30.25
## [58] jsonlite_1.8.9 R6_2.5.1 fs_1.6.4
## [61] zlibbioc_1.51.2- Installation
- Motivation
- A Brief Description
- Overview of the
ExperimentSubsetclass - Core methods of
ExperimentSubsetclass - Using the
ExperimentSubsetobject: A toy example - Using
the
ExperimentSubsetobject: An example with real single cell RNA-seq data - Supported Input Object Classes
- Methods for
ExperimentSubset - Implementation Details
- Session Information