biosigner: A new method for signature discovery from omics data
26 June 2025
Package
biosigner 1.36.2
1 Introduction
High-throughput, non-targeted, technologies such as transcriptomics, proteomics and metabolomics, are widely used to discover molecules which allow to efficiently discriminate between biological or clinical conditions of interest (e.g., disease vs control states). Powerful machine learning approaches such as Partial Least Square Discriminant Analysis (PLS-DA), Random Forest (RF) and Support Vector Machines (SVM) have been shown to achieve high levels of prediction accuracy. Feature selection, i.e., the selection of the few features (i.e., the molecular signature) which are of highest discriminating value, is a critical step in building a robust and relevant classifier (Guyon and Elisseeff 2003): First, dimension reduction is usefull to limit the risk of overfitting and increase the prediction stability of the model; second, intrepretation of the molecular signature is facilitated; third, in case of the development of diagnostic product, a restricted list is required for the subsequent validation steps (Rifai, Gillette, and Carr 2006).
Since the comprehensive analysis of all combinations of features is not computationally tractable, several selection techniques have been described, including filter (e.g., p-values thresholding), wrapper (e.g., recursive feature elimination), and embedded (e.g., sparse PLS) approaches (Saeys, Inza, and Larranaga 2007). The major challenge for such methods is to be fast and extract restricted and stable molecular signatures which still provide high performance of the classifier (Gromski et al. 2014; Determan 2015).
2 The biosigner package
The
biosigner
package implements a new wrapper feature selection algorithm:
the dataset is split into training and testing subsets (by bootstraping, controling class proportion),
model is trained on the training set and balanced accuracy is evaluated on the test set,
the features are ranked according to their importance in the model,
the relevant feature subset at level f is found by a binary search: a feature subset is considered relevant if and only if, when randomly permuting the intensities of other features in the test subsets, the proportion of increased or equal prediction accuracies is lower than a defined threshold f,
the dataset is restricted to the selected features and steps 1 to 4 are repeated until the selected list of features is stable.
Three binary classifiers have been included in
biosigner,
namely PLS-DA, RF and SVM, as the performances of each
machine learning approach may vary depending on the structure of the
dataset (Determan 2015). The algorithm returns the tier of each
feature for the selected classifer(s): tier S corresponds to the
final signature, i.e., features which have been found significant in
all the selection steps; features with tier A have been found
significant in all but the last selection, and so on for tier B to
D. Tier E regroup all previous round of selection.
As for a classical classification algorithm, the biosign method takes
as input the x samples times features data frame (or matrix) of
intensities, and the y factor (or character vector) of class labels
(note that only binary classification is currently available). It
returns the signature (signatureLs: selected feature names) and the
trained model (modelLs) for each of the selected classifier. The
plot method for biosign objects enable to visualize the individual
boxplots of the selected features. Finally, the predict method allows
to apply the trained classifier(s) on new datasets.
The algorithm has been successfully applied to transcriptomics and metabolomics data [Rinaudo et al. (2016); see also the Hands-on section below).
3 Hands-on
3.1 Loading
We first load the
biosigner
package:
library(biosigner)We then use the diaplasma metabolomics dataset (Rinaudo et al. 2016)
which results from the analysis of plasma samples from 69 diabetic
patients were analyzed by reversed-phase liquid chromatography coupled
to high-resolution mass spectrometry (LC-HRMS; Orbitrap Exactive) in
the negative ionization mode. The raw data were pre-processed with XCMS
and CAMERA (5,501 features), corrected for signal drift, log10
transformed, and annotated with an in-house spectral database. The
patient’s age, body mass index, and diabetic type are
recorded (Rinaudo et al. 2016).
data(diaplasma)We attach diaplasma to the search path and display a summary of the
content of the dataMatrix, sampleMetadata and variableMetadata
with the view function from the (imported)
ropls
package:
attach(diaplasma)
library(ropls)
ropls::view(dataMatrix)## dim class mode typeof size NAs min mean median max
## 69 x 5,501 matrix numeric double 3.3 Mb 0 0 4.2 4.4 8.2
## m096.009t01.6 m096.922t00.8 ... m995.603t10.2 m995.613t10.2
## DIA001 2.98126177377087 6.08172882312848 ... 3.93442594703862 3.96424920154706
## DIA002 0 6.13671997362279 ... 3.74201112636229 3.78128422428722
## ... ... ... ... ... ...
## DIA077 0 6.12515971273103 ... 4.55458598372024 4.57310800324247
## DIA078 4.69123816772499 6.134420482337 ... 4.1816445335704 4.20696191303494
ropls::view(sampleMetadata, standardizeL = TRUE)## type age bmi
## factor numeric numeric
## nRow nCol size NAs
## 69 3 0 Mb 0
## type age bmi
## DIA001 T2 70 31.6
## DIA002 T2 67 28
## ... ... ... ...
## DIA077 T2 50 27
## DIA078 T2 65 29## 1 data.frame 'factor' column(s) converted to 'numeric' for plotting.## Standardization of the columns for plotting.
ropls::view(variableMetadata, standardizeL = TRUE)## mzmed rtmed ... pcgroup spiDb
## numeric numeric ... numeric character
## nRow nCol size NAs
## 5,501 6 0.8 Mb 0
## mzmed rtmed ... pcgroup
## m096.009t01.6 96.00899361 93.92633015 ... 1984
## m096.922t00.8 96.92192011 48.93274877 ... 4
## ... ... ... ... ...
## m995.603t10.2 995.6030195 613.4388762 ... 7160
## m995.613t10.2 995.6134422 613.4446705 ... 7161
## spiDb
## m096.009t01.6 N-Acetyl-L-aspartic acid_HMDB00812
## m096.922t00.8
## ... ...
## m995.603t10.2
## m995.613t10.2## 3 data.frame 'character' column(s) converted to 'numeric' for plotting.
## Standardization of the columns for plotting.
We see that the diaplasma list contains three objects:
dataMatrix: 69 samples x 5,501 matrix of numeric type containing the intensity profiles (log10 transformed),sampleMetadata: a 69 x 3 data frame, with the patients’type: diabetic type, factorage: numericbmi: body mass index, numeric
variableMetadata: a 5,501 x 8 data frame, with the median m/z (‘mzmed’, numeric) and the median retention time in seconds (‘rtmed’, numeric) from XCMS, the ‘isotopes’ (character), ‘adduct’ (character) and ‘pcgroups’ (numeric) annotations from CAMERA, the names of the m/z and RT matching compounds from an in-house spectra of commercial metabolites (‘name_hmdb’, character), and the p-values resulting from the non-parametric hypothesis testing of difference in medians between types (‘type_wilcox_fdr’, numeric), and correlation with age (‘age_spearman_fdr’, numeric) and body mass index (‘bmi_spearman_fdr’, numeric), all corrected for multiple testing (False Discovery Rate).se: The previous data and metadata as aSummarizedExperimentinstanceesetThe previous data as aExpressionSetinstance
We can observe that the 3 clinical covariates (diabetic type, age, and bmi) are stronlgy associated:
with(sampleMetadata,
plot(age, bmi, cex = 1.5, col = ifelse(type == "T1", "blue", "red"), pch = 16))
legend("topleft", cex = 1.5, legend = paste0("T", 1:2),
text.col = c("blue", "red"))
Figure 1: age, body mass index (bmi), and diabetic type of
the patients from the diaplasma cohort.
3.2 Molecular signatures
Let us look for signatures of type in the diaplasma dataset by using
the biosign method. To speed up computations in this demo vignette, we
restrict the number of features (from 5,501 to about 500) and the number
of bootstraps (5 instead of 50 [default]); the selection on the whole
dataset, 50 bootstraps, and the 3 classifiers, takes around 10 min.
featureSelVl <- variableMetadata[, "mzmed"] >= 450 &
variableMetadata[, "mzmed"] < 500
sum(featureSelVl)## [1] 533dataMatrix <- dataMatrix[, featureSelVl]
variableMetadata <- variableMetadata[featureSelVl, ]diaSign <- biosign(dataMatrix, sampleMetadata[, "type"], bootI = 5)## Selecting features for the plsda model
## Selecting features for the randomforest model
## Selecting features for the svm model
## Significant features from 'S' groups:
## plsda randomforest svm
## m495.261t08.7 "C" "A" "S"
## m497.284t08.1 "S" "S" "E"
## m497.275t08.1 "A" "S" "E"
## m471.241t07.6 "B" "S" "E"
## Accuracy:
## plsda randomforest svm
## Full 0.797 0.835 0.824
## AS 0.823 0.845 0.708
## S 0.825 0.858 0.708
Figure 2: Relevant signatures for the PLS-DA, Random Forest, and
SVM classifiers extracted from the diaplasma dataset. The S tier
corresponds to the final metabolite signature, i.e., metabolites which
passed through all the selection steps.
The arguments are:
x: the numerical matrix (or data frame) of intensities (samples as rows, variables as columns),y: the factor (or character) specifying the sample labels from the 2 classes,methodVc: the classifier(s) to be used; here, the default all value means that all classifiers available (plsda, randomforest, and svm) are selected,bootI: the number of bootstraps is set to 5 to speed up computations when generating this vignette; we however recommend to keep the default 50 value for your analyzes (otherwise signatures may be less stable).The
set.seedargument ensures that the results from this vignette can be reproduced exactly; by choosing alternative seeds (and the defaultbootI= 50), similar signatures are obtained, showing the stability of the selection.
Note:
- If some features from the
xmatrix/data frame contain missing values (NA), these features will be removed prior to modeling with Random Forest and SVM (in contrast, the NIPALS algorithm from PLS-DA can handle missing values),
The resulting signatures for the 3 selected classifiers are both printed and plotted as tiers from S, A, up to E by decreasing relevance. The (S) tier corresponds to the final signature, i.e. features which passed through all the backward selection steps. In contrast, features from the other tiers were discarded during the last (A) or previous (B to E) selection rounds.
Note that tierMaxC = ‘A’ argument in the print and plot methods can be used to view the features from the larger S+A signatures (especially when no S features have been found, or when the performance of the S model is much lower than the S+A model).
The performance of the model built with the input dataset (balanced accuracy: mean of the sensitivity and specificity), or the subset restricted to the S or S+A signatures are shown. We see that with 1 to 5 S feature signatures (i.e., less than 1% of the input), the 3 classifiers achieve good performances (even higher than the full Random Forest and SVM models). Furthermore, reducing the number of features decreases the risk of building non-significant models (i.e., models which do not perform significantly better than those built after randomly permuting the labels). The signatures from the 3 classifiers have some distinct features, which highlights the interest of comparing various machine learning approaches.
The individual boxplots of the features from the complete signature can be visualized with:
plot(diaSign, typeC = "boxplot")
Figure 3: Individual boxplots of the features selected for at least one of the classification methods. Features selected for a single classifier are colored (red for PLS-DA, green for Random Forest and blue for SVM).
Let us see the metadata of the complete signature:
variableMetadata[getSignatureLs(diaSign)[["complete"]], ]## mzmed rtmed isotopes adduct pcgroup
## m495.261t08.7 495.2609 524.1249 1655
## m497.284t08.1 497.2840 486.5338 [M+Cl]- 462.31 [M-H]- 498.287 220
## m497.275t08.1 497.2755 486.5722 [M+Cl]- 462.31 [M-H]- 498.287 220
## m471.241t07.6 471.2408 455.5541 10538
## spiDb
## m495.261t08.7
## m497.284t08.1
## m497.275t08.1 Taurochenodeoxycholic acid_HMDB00951
## m471.241t07.63.3 Predictions
Let us split the dataset into a training (the first 4/5th of the 183 samples) and a testing subsets, and extract the relevant features from the training subset:
trainVi <- 1:floor(0.8 * nrow(dataMatrix))
testVi <- setdiff(1:nrow(dataMatrix), trainVi)diaTrain <- biosign(dataMatrix[trainVi, ], sampleMetadata[trainVi, "type"],
bootI = 5)## Selecting features for the plsda model
## Selecting features for the randomforest model
## Selecting features for the svm model
## Significant features from 'S' groups:
## plsda randomforest svm
## m497.284t08.1 "S" "S" "E"
## m469.215t07.8 "E" "E" "S"
## Accuracy:
## plsda randomforest svm
## Full 0.753 0.797 0.728
## AS 0.823 0.855 0.668
## S 0.814 0.782 0.603
Figure 4: Signatures from the training data set.
We extract the fitted types on the training dataset restricted to the S signatures:
diaFitDF <- predict(diaTrain)We then print the confusion tables for each classifier:
lapply(diaFitDF, function(predFc) table(actual = sampleMetadata[trainVi,
"type"], predicted = predFc))## $plsda
## predicted
## actual T1 T2
## T1 16 6
## T2 4 29
##
## $randomforest
## predicted
## actual T1 T2
## T1 14 8
## T2 7 26
##
## $svm
## predicted
## actual T1 T2
## T1 7 15
## T2 3 30and the corresponding balanced accuracies:
sapply(diaFitDF, function(predFc) {
conf <- table(sampleMetadata[trainVi, "type"], predFc)
conf <- sweep(conf, 1, rowSums(conf), "/")
round(mean(diag(conf)), 3)
})## plsda randomforest svm
## 0.803 0.712 0.614Note that these values are slightly different from the accuracies returned by biosign because the latter are computed by using the resampling scheme selected by the bootI (or crossvalI) arguments:
round(getAccuracyMN(diaTrain)["S", ], 3)## plsda randomforest svm
## 0.814 0.782 0.603Finally, we can compute the performances on the test subset:
diaTestDF <- predict(diaTrain, newdata = dataMatrix[testVi, ])
sapply(diaTestDF, function(predFc) {
conf <- table(sampleMetadata[testVi, "type"], predFc)
conf <- sweep(conf, 1, rowSums(conf), "/")
round(mean(diag(conf)), 3)
})## plsda randomforest svm
## 0.750 0.667 0.5003.4 Working on SummarizedExperiment objects
The SummarizedExperiment class from the
SummarizedExperiment
bioconductor package has been developed to conveniently handle
preprocessed omics objects, including the variable x sample matrix of
intensities, and two DataFrames containing the sample and variable
metadata, which can be accessed by the assay, colData and rowData
methods respectively (remember that the data matrix is stored with
samples in columns).
Getting the diaplasma dataset as a SummarizedExperiment:
# Preparing the data (matrix) and sample and variable metadata (data frames):
data(diaplasma)
data.mn <- diaplasma[["dataMatrix"]] # matrix: samples x variables
samp.df <- diaplasma[["sampleMetadata"]] # data frame: samples x sample metadata
feat.df <- diaplasma[["variableMetadata"]] # data frame: features x feature metadata
# Creating the SummarizedExperiment (package SummarizedExperiment)
library(SummarizedExperiment)
dia.se <- SummarizedExperiment(assays = list(diaplasma = t(data.mn)),
colData = samp.df,
rowData = feat.df)
# note that colData and rowData main format is DataFrame, but data frames are accepted when building the object
stopifnot(validObject(dia.se))
# Viewing the SummarizedExperiment
# ropls::view(dia.se)The biosign method can be applied to a SummarizedExperiment
object, by using the object as the x argument, and by indicating as
the y argument the name of the sample metadata to be used as the
response (i.e. name of the column in the colData). Note that in the
example below, we restrict the data set to the first 100 features to
speed up computations:
dia.se <- dia.se[1:100, ]
dia.se <- biosign(dia.se, "type", bootI = 5)
The biosign method returns the updated SummarizedExperiment
object with the tiers as new columns in the rowData
feat.DF <- SummarizedExperiment::rowData(dia.se)
head(feat.DF[, grep("type_", colnames(feat.DF))])## DataFrame with 6 rows and 3 columns
## type_biosign_plsda type_biosign_forest type_biosign_svm
## <character> <character> <character>
## m096.009t01.6 E E B
## m096.922t00.8 E E E
## m098.025t01.3 E E E
## m099.009t01.3 E B E
## m099.009t00.9 E E E
## m099.045t04.0 E A Eand with the biosign model in the metadata slot, which can be
accessed with the getBiosign method:
dia_type.biosign <- getBiosign(dia.se)
names(dia_type.biosign)## [1] "type_plsda.forest.svm"plot(dia_type.biosign[["type_plsda.forest.svm"]], typeC = "tier")
3.4.1 ExpressionSet format
The ExpressionSet format is currently supported as a legacy
representation from the previous versions of the biosigner package (<
1.24.2) but will now be supplanted by SummarizedExperiment in future
versions.
exprs, pData, and fData for ExpressionSet are similar to
assay, colData and rowData for SummarizedExperiment except that
assay is a list which can potentially include several matrices, and
that colData and rowData are of the DataFrame format.
SummarizedExperiment format further enables to store additional
metadata (such as models or ggplots) in a dedicated metadata slot.
In the example below, we will first build a minimal ExpressionSet
object from the diaplasma data set and view the data, and we
subsequently perform the feature selection.
Getting the diaplasma data set as a ExpressionSet:
# Preparing the data (matrix) and sample and variable metadata (data frames):
data(diaplasma)
data.mn <- diaplasma[["dataMatrix"]] # matrix: samples x variables
samp.df <- diaplasma[["sampleMetadata"]] # data frame: samples x sample metadata
feat.df <- diaplasma[["variableMetadata"]] # data frame: features x feature metadata
# Creating the SummarizedExperiment (package SummarizedExperiment)
library(Biobase)
dia.eset <- Biobase::ExpressionSet(assayData = t(data.mn))
Biobase::pData(dia.eset) <- samp.df
Biobase::fData(dia.eset) <- feat.df
stopifnot(validObject(dia.eset))
# Viewing the ExpressionSet
# ropls::view(dia.eset)Selecting the features:
dia.eset <- dia.eset[1:100, ]
dia_type.biosign <- biosign(dia.eset, "type", bootI = 5)
Note that this time, biosign returns the models an en object of the
biosign class.
plot(dia_type.biosign, typeC = "tier")
The updated ExpressionSet object can be accessed with the getEset
method:
dia.eset <- getEset(dia_type.biosign)
feat.df <- Biobase::fData(dia.eset)
head(feat.df[, grep("type_", colnames(feat.df))])## type_biosign_plsda type_biosign_forest type_biosign_svm
## m096.009t01.6 E E B
## m096.922t00.8 E E E
## m098.025t01.3 E E E
## m099.009t01.3 E B E
## m099.009t00.9 E E E
## m099.045t04.0 E A EBefore moving to new data sets, we detach diaplasma from the search path:
detach(diaplasma)3.5 Working on MultiAssayExperiment objects
The MultiAssayExperiment format is useful to handle multi-omics
data sets (???). Feature selection
can be performed in parallel for each data set by applying opls to
such formats. We provide an example based on the NCI60_4arrays cancer
data set from the omicade4 package (which has been made available in
this ropls package in the MultiAssayExperiment format).
Getting the NCI60 data set as a MultiAssayExperiment:
data("NCI60", package = "ropls")
nci.mae <- NCI60[["mae"]]
library(MultiAssayExperiment)
# Cancer types
table(nci.mae$cancer)##
## BR CN CO LC LE ME OV PR RE
## 5 6 7 9 6 10 7 2 8# Restricting to the 'ME' and 'LE' cancer types and to the 'agilent' and 'hgu95' datasets
nci.mae <- nci.mae[, nci.mae$cancer %in% c("ME", "LE"), c("agilent", "hgu95")]## Warning: 'experiments' dropped; see 'drops()'Performing the feature selection for each dataset:
nci.mae <- biosign(nci.mae, "cancer", bootI = 5)##
##
## Selecting the features for the 'agilent' dataset:
## Selecting features for the plsda model
## Selecting features for the randomforest model
## Selecting features for the svm model
## Significant features from 'S' groups:
## plsda randomforest svm
## VEPH1 "S" "E" "B"
## LHFP "S" "E" "B"
## C10orf90 "B" "E" "S"
## EZH2 "E" "S" "E"
## Accuracy:
## plsda randomforest svm
## Full 1 1.000 1.000
## AS 1 0.900 0.983
## S 1 0.917 0.983
##
##
## Selecting the features for the 'hgu95' dataset:
## Selecting features for the plsda model
## Selecting features for the randomforest model
## Selecting features for the svm model
## Significant features from 'S' groups:
## plsda randomforest svm
## TSPAN4 "S" "S" "E"
## TBC1D16 "S" "E" "B"
## NASP "S" "E" "E"
## Accuracy:
## plsda randomforest svm
## Full 1 1 1.000
## AS 1 1 0.917
## S 1 1 NA
The biosigner method returns an updated MultiAssayExperiment with
the tiers included as additional columns in the rowData of the
individual SummarizedExperiment:
SummarizedExperiment::rowData(nci.mae[["agilent"]])## DataFrame with 300 rows and 4 columns
## name cancer_biosign_plsda cancer_biosign_forest
## <character> <character> <character>
## ST8SIA1 ST8SIA1 E E
## YWHAQ YWHAQ E E
## EPHA4 EPHA4 E E
## GTPBP5 GTPBP5 E E
## PVR PVR E E
## ... ... ... ...
## HIST1H2AB HIST1H2AB E E
## XPO6 XPO6 E E
## KIAA1688 KIAA1688 E E
## TCEAL2 TCEAL2 B E
## GLCCI1 GLCCI1 E E
## cancer_biosign_svm
## <character>
## ST8SIA1 B
## YWHAQ E
## EPHA4 B
## GTPBP5 E
## PVR E
## ... ...
## HIST1H2AB E
## XPO6 E
## KIAA1688 E
## TCEAL2 E
## GLCCI1 EThe biosign model(s) are stored in the metadata of the individual
SummarizedExperiment objects included in the MultiAssayExperiment,
and can be accessed with the getBiosign method:
mae_biosign.ls <- getBiosign(nci.mae)
for (set.c in names(mae_biosign.ls))
plot(mae_biosign.ls[[set.c]][["cancer_plsda.forest.svm"]],
typeC = "tier",
plotSubC = set.c)
3.5.1 MultiDataSet objects
The MultiDataSet format (???) is
currently supported as a legacy representation from the previous
versions of the biosigner package (<1.24.2) but will now be
supplanted by MultiAssayExperiment in future versions. Note that the
mds2mae method from the MultiDataSet package enables to convert a
MultiDataSet into the MultiAssayExperiment format.
Getting the NCI60 data set as a MultiDataSet:
data("NCI60", package = "ropls")
nci.mds <- NCI60[["mds"]]Building PLS-DA models for the cancer type:
# Restricting to the "agilent" and "hgu95" datasets
nci.mds <- nci.mds[, c("agilent", "hgu95")]
# Restricting to the 'ME' and 'LE' cancer types
library(Biobase)
sample_names.vc <- Biobase::sampleNames(nci.mds[["agilent"]])
cancer_type.vc <- Biobase::pData(nci.mds[["agilent"]])[, "cancer"]
nci.mds <- nci.mds[sample_names.vc[cancer_type.vc %in% c("ME", "LE")], ]
# Selecting the features
nci_cancer.biosign <- biosign(nci.mds, "cancer", bootI = 5)
Getting back the updated MultiDataSet:
nci.mds <- getMset(nci_cancer.biosign)4 Extraction of biomarker signatures from other omics datasets
In this section, biosign is applied to two metabolomics and one
transcriptomics data sets. Please refer to Rinaudo et al. (2016) for a full
discussion of the methods and results.
4.1 Physiological variations of the human urine metabolome (metabolomics)
The sacurine LC-HRMS dataset from the dependent
ropls
package can also be used (Thevenot et al. 2015): Urine samples from a cohort of
183 adults were analyzed by using an LTQ Orbitrap in the negative
ionization mode. A total of 109 metabolites were identified or annotated
at the MSI level 1 or 2. Signal drift and batch effect were corrected,
and each urine profile was normalized to the osmolality of the sample.
Finally, the data were log10 transformed (see the
ropls
vignette for further details and examples).
We can for instance look for signatures of the gender:
data(sacurine)
sacSign <- biosign(sacurine[["dataMatrix"]],
sacurine[["sampleMetadata"]][, "gender"],
methodVc = "plsda")## Selecting features for the plsda model
## Significant features from 'S' groups:
## plsda
## Malic acid "S"
## p-Anisic acid "S"
## Testosterone glucuronide "S"
## Accuracy:
## plsda
## Full 0.876
## AS 0.882
## S 0.889
Figure 5: PLS-DA signature from the ‘sacurine’ data set.
4.2 Apples spikes with known compounds (metabolomics)
The spikedApples dataset was obtained by LC-HRMS analysis (SYNAPT Q-TOF, Waters) of one control and three spiked groups of 10 apples each. The spiked mixtures consists in 2 compounds which were not naturally present in the matrix and 7 compounds aimed at achieving a final increase of 20%, 40% or 100% of the endogeneous concentrations. The authors identified 22 features (out of the 1,632 detected in the positive ionization mode; i.e. 1.3%) which came from the spiked compounds. The dataset is borrowed from the BioMark R package (Franceschi et al. 2012). Let us use the control and group1 samples (20 in total) in this study.
data(SpikePos)
group1Vi <- which(SpikePos[["classes"]] %in% c("control", "group1"))
appleMN <- SpikePos[["data"]][group1Vi, ]
spikeFc <- factor(SpikePos[["classes"]][group1Vi])
annotDF <- SpikePos[["annotation"]]
rownames(annotDF) <- colnames(appleMN)We can check, by using the opls method from the
ropls
package for multivariate analysis, that:
- no clear separation can be observed by PCA:
apple.pca <- ropls::opls(appleMN, fig.pdfC = "none")## PCA
## 20 samples x 1632 variables
## standard scaling of predictors
## R2X(cum) pre ort
## Total 0.523 7 0ropls::plot(apple.pca, parAsColFcVn = spikeFc)
- PLS-DA modeling with the full dataset is not significant (as seen on the top left plot: 7 out of 20 models trained after random permutations of the labels have Q2 values higher than the model trained with the true labels):
apple.pls <- ropls::opls(appleMN, spikeFc)## PLS-DA
## 20 samples x 1632 variables and 1 response
## standard scaling of predictors and response(s)
## R2X(cum) R2Y(cum) Q2(cum) RMSEE pre ort pR2Y pQ2
## Total 0.145 0.995 0.4 0.0396 2 0 0.05 0.55
Let us now extract the molecular signatures:
appleSign <- biosign(appleMN, spikeFc)## Selecting features for the plsda model
## Selecting features for the randomforest model
## Selecting features for the svm model
## Significant features from 'S' groups:
## plsda randomforest svm
## 449.1/327 "S" "S" "C"
## Accuracy:
## plsda randomforest svm
## Full 0.79 0.921 0.793
## AS 1.00 1.000 0.853
## S 1.00 1.000 NA
The 449.1/327 corresponds to the Cyanidin-3-galactoside (absent in the control; Franceschi et al. (2012)).
annotDF <- SpikePos[["annotation"]]
rownames(annotDF) <- colnames(appleMN)
annotDF[getSignatureLs(appleSign)[["complete"]], c("adduct", "found.in.standards")]## adduct found.in.standards
## 449.1/327 14.3 Bone marrow from acute leukemia patients (transcriptomics)
Samples from 47 patients with acute lymphoblastic leukemia (ALL) and 25
patients with acute myeloid leukemia (AML) have been analyzed using
Affymetrix Hgu6800 chips resulting in expression data of 7,129 gene
probes (Golub et al. 1999). The golub dataset is available in the
golubEsets
package from Bioconductor in the ExpressionSet format. Let us compute
for example the SVM signature (to speed up this demo example, the number
of features is restricted to 500):
library(golubEsets)
data(Golub_Merge)
Golub_Merge## ExpressionSet (storageMode: lockedEnvironment)
## assayData: 7129 features, 72 samples
## element names: exprs
## protocolData: none
## phenoData
## sampleNames: 39 40 ... 33 (72 total)
## varLabels: Samples ALL.AML ... Source (11 total)
## varMetadata: labelDescription
## featureData: none
## experimentData: use 'experimentData(object)'
## pubMedIds: 10521349
## Annotation: hu6800# restricting to the last 500 features
golub.eset <- Golub_Merge[1501:2000, ]
table(Biobase::pData(golub.eset)[, "ALL.AML"])##
## ALL AML
## 47 25golubSign <- biosign(golub.eset, "ALL.AML", methodVc = "svm")## Selecting features for the svm model
## Significant features from 'S' groups:
## svm
## M11147_at "S"
## M17733_at "S"
## M19507_at "S"
## M27891_at "S"
## Accuracy:
## svm
## Full 0.955
## AS 0.967
## S 0.959
Figure 6: SVM signature from the golub data set.
The computation results in a signature of 4 features only and a sparse SVM model performing even better (95.9% accuracy) than the model trained on the dataset of 500 variables (95.5% accuracy).
The hu6800.db bioconductor package can be used to get the annotation of the selected probes (Carlson 2016):
library(hu6800.db)
sapply(getSignatureLs(golubSign)[["complete"]],
function(probeC)
get(probeC, env = hu6800GENENAME))## M11147_at M17733_at
## "ferritin light chain" "thymosin beta 4 X-linked"
## M19507_at M27891_at
## "myeloperoxidase" "cystatin C"Cystatin C is part of the 50 gene signature selected by Golub and colleagues on the basis of a metric derived from the Student’s statistic of mean differences between the AML and ALL groups (Golub et al. 1999). Interestingly, the third probe, myeloperoxidase, is a cytochemical marker for the diagnosis (and also potentially the prognosis) of acute myeloid leukemia (AML).
5 Session info
Here is the output of sessionInfo() on the system on which this
document was compiled:
## R version 4.5.1 (2025-06-13 ucrt)
## Platform: x86_64-w64-mingw32/x64
## Running under: Windows Server 2022 x64 (build 20348)
##
## Matrix products: default
## LAPACK version 3.12.1
##
## locale:
## [1] LC_COLLATE=C
## [2] LC_CTYPE=English_United States.utf8
## [3] LC_MONETARY=English_United States.utf8
## [4] LC_NUMERIC=C
## [5] LC_TIME=English_United States.utf8
##
## time zone: America/New_York
## tzcode source: internal
##
## attached base packages:
## [1] stats4 stats graphics grDevices utils datasets methods
## [8] base
##
## other attached packages:
## [1] hu6800.db_3.13.0 org.Hs.eg.db_3.21.0
## [3] AnnotationDbi_1.70.0 golubEsets_1.50.0
## [5] MultiAssayExperiment_1.34.0 SummarizedExperiment_1.38.1
## [7] Biobase_2.68.0 GenomicRanges_1.60.0
## [9] GenomeInfoDb_1.44.0 IRanges_2.42.0
## [11] S4Vectors_0.46.0 BiocGenerics_0.54.0
## [13] generics_0.1.4 MatrixGenerics_1.20.0
## [15] matrixStats_1.5.0 ropls_1.40.0
## [17] biosigner_1.36.2 BiocStyle_2.36.0
##
## loaded via a namespace (and not attached):
## [1] KEGGREST_1.48.1 MultiDataSet_1.36.0 xfun_0.52
## [4] bslib_0.9.0 lattice_0.22-7 vctrs_0.6.5
## [7] tools_4.5.1 proxy_0.4-27 RSQLite_2.4.1
## [10] blob_1.2.4 pkgconfig_2.0.3 BiocBaseUtils_1.10.0
## [13] Matrix_1.7-3 lifecycle_1.0.4 GenomeInfoDbData_1.2.14
## [16] compiler_4.5.1 Biostrings_2.76.0 statmod_1.5.0
## [19] tinytex_0.57 htmltools_0.5.8.1 class_7.3-23
## [22] sass_0.4.10 yaml_2.3.10 crayon_1.5.3
## [25] jquerylib_0.1.4 MASS_7.3-65 DelayedArray_0.34.1
## [28] cachem_1.1.0 limma_3.64.1 magick_2.8.7
## [31] abind_1.4-8 digest_0.6.37 bookdown_0.43
## [34] fastmap_1.2.0 grid_4.5.1 cli_3.6.5
## [37] SparseArray_1.8.0 magrittr_2.0.3 S4Arrays_1.8.1
## [40] randomForest_4.7-1.2 e1071_1.7-16 UCSC.utils_1.4.0
## [43] bit64_4.6.0-1 calibrate_1.7.7 rmarkdown_2.29
## [46] XVector_0.48.0 httr_1.4.7 bit_4.6.0
## [49] png_0.1-8 memoise_2.0.1 evaluate_1.0.4
## [52] knitr_1.50 qqman_0.1.9 rlang_1.1.6
## [55] Rcpp_1.0.14 DBI_1.2.3 BiocManager_1.30.26
## [58] jsonlite_2.0.0 R6_2.6.1References
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