SEtools

Pierre-Luc Germain, 14.01.2020

D-HEST Institute for Neurosciences, ETH Zürich & Laboratory of Statistical Bioinformatics, University Zürich

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The SEtools package is a set of convenience functions for the Bioconductor class SummarizedExperiment. It facilitates merging, melting, and plotting SummarizedExperiment objects.

NOTE that the heatmap-related functions habe been moved to a standalone package, sechm, and have been deprecated from this package.

Getting started

Package installation

if (!requireNamespace("BiocManager", quietly = TRUE))
    install.packages("BiocManager")
BiocManager::install("SEtools")

Or, to install the latest development version:

BiocManager::install("plger/SEtools")

Example data

To showcase the main functions, we will use an example object which contains (a subset of) whole-hippocampus RNAseq of mice after different stressors:

suppressPackageStartupMessages({
  library(SummarizedExperiment)
  library(SEtools)
})
data("SE", package="SEtools")
SE

## class: SummarizedExperiment 
## dim: 100 20 
## metadata(0):
## assays(2): counts logcpm
## rownames(100): Egr1 Nr4a1 ... CH36-200G6.4 Bhlhe22
## rowData names(2): meanCPM meanTPM
## colnames(20): HC.Homecage.1 HC.Homecage.2 ... HC.Swim.4 HC.Swim.5
## colData names(2): Region Condition

This is taken from Floriou-Servou et al., Biol Psychiatry 2018.

Merging and aggregating SEs

se1 <- SE[,1:10]
se2 <- SE[,11:20]
se3 <- mergeSEs( list(se1=se1, se2=se2) )
se3

## class: SummarizedExperiment 
## dim: 100 20 
## metadata(3): se1 se2 anno_colors
## assays(2): counts logcpm
## rownames(100): AC139063.2 Actr6 ... Zfp667 Zfp930
## rowData names(3): meanCPM meanTPM cluster
## colnames(20): se1.HC.Homecage.1 se1.HC.Homecage.2 ...
##   se2.HC.Swim.4 se2.HC.Swim.5
## colData names(3): Dataset Region Condition

All assays were merged, along with rowData and colData slots.

By default, row z-scores are calculated for each object when merging. This can be prevented with:

se3 <- mergeSEs( list(se1=se1, se2=se2), do.scale=FALSE)

If more than one assay is present, one can specify a different scaling behavior for each assay:

se3 <- mergeSEs( list(se1=se1, se2=se2), use.assays=c("counts", "logcpm"), do.scale=c(FALSE, TRUE))

Merging by rowData columns

It is also possible to merge by rowData columns, which are specified through the mergeBy argument. In this case, one can have one-to-many and many-to-many mappings, in which case two behaviors are possible:

• By default, all combinations will be reported, which means that the same feature of one object might appear multiple times in the output because it matches multiple features of another object.
• If a function is passed through aggFun, the features of each object will by aggregated by mergeBy using this function before merging.

rowData(se1)$metafeature <- sample(LETTERS,nrow(se1),replace = TRUE)
rowData(se2)$metafeature <- sample(LETTERS,nrow(se2),replace = TRUE)
se3 <- mergeSEs( list(se1=se1, se2=se2), do.scale=FALSE, mergeBy="metafeature", aggFun=median)

## Aggregating the objects by metafeature
## Merging...

sehm(se3)

Aggregating a SE

A single SE can also be aggregated by using the aggSE function:

se1b <- aggSE(se1, by = "metafeature")

## Aggregation methods for each assay:
## counts: sum; logcpm: expsum

se1b

## class: SummarizedExperiment 
## dim: 26 10 
## metadata(0):
## assays(2): counts logcpm
## rownames(26): A B ... Y Z
## rowData names(4): meanCPM meanTPM cluster metafeature
## colnames(10): HC.Homecage.1 HC.Homecage.2 ... HC.Handling.4
##   HC.Handling.5
## colData names(2): Region Condition

If the aggregation function(s) are not specified, aggSE will try to guess decent aggregation functions from the assay names.

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Melting SE

To facilitate plotting features with ggplot2, the meltSE function combines assay values along with row/column data:

d <- meltSE(SE, genes=g[1:4])
head(d)

##   feature        sample Region Condition counts    logcpm
## 1    Egr1 HC.Homecage.1     HC  Homecage 1581.0 4.4284969
## 2   Nr4a1 HC.Homecage.1     HC  Homecage  750.0 3.6958917
## 3     Fos HC.Homecage.1     HC  Homecage   91.4 1.7556317
## 4    Egr2 HC.Homecage.1     HC  Homecage   15.1 0.5826999
## 5    Egr1 HC.Homecage.2     HC  Homecage 1423.0 4.4415828
## 6   Nr4a1 HC.Homecage.2     HC  Homecage  841.0 3.9237691

suppressPackageStartupMessages(library(ggplot2))
ggplot(d, aes(Condition, counts, fill=Condition)) + geom_violin() + 
    facet_wrap(~feature, scale="free")