--- title: "MultiAssayExperiment primary vignette" author: "MultiAssay Special Interest Group" date: "`r format(Sys.time(), '%B %d, %Y')`" output: html_document: number_sections: yes toc: yes vignette: > %\VignetteEngine{knitr::rmarkdown} %\VignetteIndexEntry{Coordinating Analysis of Multi-Assay Experiments} --- A built [html][] version of this vignette is available. ```{r, echo=FALSE, warning=FALSE} suppressPackageStartupMessages(library(MultiAssayExperiment)) ``` # API See the API wiki by typing: ```{r, eval=FALSE} API() ``` A Shiny App that browses the API is also available: ```{r, eval=FALSE} API(shiny=TRUE) ``` # Overview of the `MultiAssayExperiment` class Here is an overview of the class and its constructors and extractors: ```{r} empty <- MultiAssayExperiment() empty slotNames(empty) ``` We explain the role of each of these components of `MultiAssayExperiment` below. ## Elist: experimental data The `Elist` slot and class is the driver for the `MultiAssayExperiment` class, as it contains the experimental data. It is a `SimpleList` (similar to the base `list`), with one element per data type. ```{r} class(Elist(empty)) # Elist ``` The elements of `Elist` can contain **ID-based** and **range-based** data class that support a minimum of methods, see `API()` for details on using data classes not discussed here. The following classes are known to work as `Elist` elements, to support a good variety of data types: - `matrix`: the base data class, can be used for ID-based datasets such as gene expression summarized per-gene, microRNA, metabolomics, or microbiome data. - `ExpressionSet`: A richer representation for ID-based datasets, could be used for the same types of data as `matrix`, but storing additional assay-level metadata. - `SummarizedExperiment`: Another rich representation for ID-based matrix-like datasets - `RangedSummarizedExperiment`: For rectangular range-based datasets, meaning that one set of genomic ranges are assayed for multiple samples. Could be used for gene expression, methylation, or other data types referring to genomic positions. - `RangedRaggedAssay`: inherits from `GRangesList`, for ranged-based ragged arrays, meaning that a potentially different set of genomic ranges are assayed for each sample. A typical example would be segmented copy number, where segmentation of copy number alterations occurs and different genomic locations in each sample. The datasets contained in elements of `Elist` must have column names and row names. The column names correspond to samples, and are used to match assay data to specimen metadata stored in `pData`, as explained in the following two sections. - `[`: standard square bracket subsetting, with a single comma. It is assumed that values before the comma subset rows, and values after the comma subset columns. - `colnames()`: corresponding to experimental samples - `rownames()`: corresponding to features such as genes, proteins, etc - `dim()`: returns a vector of the number of rows and number of columns ## pData: primary data The `MultiAssayExperiment` keeps one set of "primary" metadata that describes the biological specimens experimental subject, patients, etc. For the sake of simplicity, we will refer to each experimental subject as a *patient*. ```{r} class(pData(empty)) # DataFrame ``` `pData` contains one row per patient or specimen, and one column per variable of clinical or experimental metadata. `rownames(pData)` must provide the identifiers used for the patients or specimens. In the following examples we will have assays for 4 patients, with the following bit of metadata relating to the patients. Although `pData` is stored internally as a `DataFrame`, the MultiAssayExperiment constructor will automatically convert a `data.frame`. ```{r} patient.data <- data.frame(sex=c("M", "F", "M", "F"), age=38:41, row.names=c("Jack", "Jill", "Bob", "Barbara")) patient.data ``` ## Note on the flexibility of the `DataFrame` For many typical purposes the `DataFrame` and `data.frame` behave equivalently; but the `Dataframe` is more flexible as it allows any vector-like data type to be stored in its columns. The flexibility of the `DataFrame` permits, for example, storing multiple dose-response values for a single cell line, even if the number of doses and responses is not consistent across all cell lines. Doses could be stored in one column of `pData` as a `SimpleList`, and responses in another column, also as a `SimpleList`. Or, dose-response values could be stored in a single column of `pData` as a two-column matrix for each cell line. ## sampleMap: relating pData to multiple assays `sampleMap` is a `DataFrame` that provides a map between the "primary" data (`pData`) and the experimental assays: ```{r} class(sampleMap(empty)) # DataFrame ``` The `sampleMap` provides an unambiguous map from every experimental observation to *one and only one* row in `pData`. It is, however, permissible for a row of `pData` to be associated with multiple experimental observations or no observations at all. In other words, there is a "many-to-one" mapping from experimental observations to rows of `pData`, and a "one-to-any-number" mapping from rows of `pData` to experimental observations. `pData` has three columns, with the following column names: 1. **primary** provides the "primary" sample names. All values in this column must also be present in the rownames of pData(MultiAssayExperiment). In this example, allowable values in this column are "Jack", "Jill", "Barbara", and "Bob". 2. **assay** provides the sample names used by experimental datasets, which in practice are often different than the primary sample names. For each assay, all column names must be found in this column. Otherwise, those assays would be orphaned: it would be impossible to match them up to samples in the overall experiment. As mentioned above, duplicated values are allowed, to represent replicates with the same overall experiment-level annotation. 3. **assayname** provides the names of the different experiments / assays performed. These are user-defined, with the only requirement that the names of the `Elist`, where the experimental assays are stored, must be contained in this column. This design is motivated by the following situations: 1. It allows flexibility for any amount of technical replication and biological replication (such as tumor and matched normal for a single patient) of individual assays. 2. It allows missing observations (such as RNA-seq performed only for some of the patients). 3. It allows the use of different identifiers to be used for patients / specimens and for each assay. These different identifiers are matched unambiguously, and consistency between them is maintained during subsetting and re-ordering. ## metadata Can be any class, for storing study-wide metadata, such as citation information. It can also be NULL, as with the empty `MultiAssayExperiment`: ```{r} class(metadata(empty)) # NULL (class "ANY") ``` ## drops Maintains provenance of rows and columns dropped during subsetting operations. # A simple example where sampleMap isn't provided If each assay uses the same colnames (ie, if the same sample identifiers are used for each experiment), a simple list of these datasets is sufficient for the `MultiAssayExperiment()` constructor function. It is not necessary for them to have the same rownames or colnames: ```{r} exprss1 <- matrix(rnorm(16), ncol = 4, dimnames = list(sprintf("ENST00000%i", sample(288754:290000, 4)), c("Jack", "Jill", "Bob", "Bobby"))) exprss2 <- matrix(rnorm(12), ncol = 3, dimnames = list(sprintf("ENST00000%i", sample(288754:290000, 4)), c("Jack", "Jane", "Bob"))) doubleExp <- list("methyl 2k" = exprss1, "methyl 3k" = exprss2) simpleMultiAssay <- MultiAssayExperiment(Elist=doubleExp) simpleMultiAssay ``` In the above example, the user did not provide the `pData` argument so the constructor function filled it with a trivial DataFrame: ```{r} pData(simpleMultiAssay) ``` But the `pData` can be provided. Here, note that any assay sample (column) that cannot be mapped to a corresponding row in the provided `pData` gets dropped. This is part of ensuring internal validity of the `MultiAssayExperiment`. ```{r} simpleMultiAssay2 <- MultiAssayExperiment(Elist=doubleExp, pData=patient.data) simpleMultiAssay2 pData(simpleMultiAssay2) ``` # Creating a `MultiAssayExperiment` object: a rich example In this section we demonstrate all core supported data classes, using different sample ID conventions for each assay, with primary pData. The currently supported classes of datasets are `matrix`, `ExpressionSet`, `SummarizedExperiment`, `RangedSummarizedExperiment`, and `RangedRaggedAssay`. ## Create toy datasets demonstrating all supported data types We have three matrix-like datasets. First let's say expression data, which in this example we represent as an `ExpressionSet`: ```{r, message=FALSE} library(Biobase) (arraydat <- matrix(seq(101, 108), ncol=4, dimnames=list(c("ENST00000294241", "ENST00000355076"), c("array1", "array2", "array3", "array4")))) arraypdat <- as(data.frame(slope53=rnorm(4), row.names=c("array1", "array2", "array3", "array4")), "AnnotatedDataFrame") exprdat <- ExpressionSet(assayData=arraydat, phenoData=arraypdat) exprdat ``` The following map matches pData sample names to exprdata sample names. Note that row orders aren't initially matched up, and this is OK. ```{r} (exprmap <- data.frame(primary=rownames(patient.data)[c(1, 2, 4, 3)], assay=c("array1", "array2", "array3", "array4"), stringsAsFactors = FALSE)) ``` Now methylation data, which we will represent as a `matrix`. It uses gene identifiers also, but measures a partially overlapping set of genes. For fun, let's store this as a simple matrix. Also, it contains a replicate for one of the patients. ```{r} (methyldat <- matrix(1:10, ncol=5, dimnames=list(c("ENST00000355076", "ENST00000383706"), c("methyl1", "methyl2", "methyl3", "methyl4", "methyl5")))) ``` The following map matches pData sample names to methyldat sample names. ```{r} (methylmap <- data.frame(primary = c("Jack", "Jack", "Jill", "Barbara", "Bob"), assay = c("methyl1", "methyl2", "methyl3", "methyl4", "methyl5"), stringsAsFactors = FALSE)) ``` Now we have a microRNA platform, which has no common identifiers with the other datasets, and which we also represent as a `matrix`. It is also missing data for Jill. Just for fun, let's use the same sample naming convention as we did for arrays. ```{r} (microdat <- matrix(201:212, ncol=3, dimnames=list(c("hsa-miR-21", "hsa-miR-191", "hsa-miR-148a", "hsa-miR148b"), c("micro1", "micro2", "micro3")))) ``` And the following map matches pData sample names to microdat sample names. ```{r} (micromap <- data.frame(primary = c("Jack", "Barbara", "Bob"), assay = c("micro1", "micro2", "micro3"), stringsAsFactors = FALSE)) ``` Let's include a `RangedRaggedAssay`, which is defined in this package and extends `GRangesList`. This is intended for data such as segmented copy number, which provide genomic ranges that may be different for each sample. We start with a `GRangesList`, which will later be converted automatically by the `MultiAssayExperiment` constructor function. ```{r} suppressPackageStartupMessages(library(GenomicRanges)) ## completely encompasses ENST00000355076 gr1 <- GRanges(seqnames = "chr3", ranges = IRanges(58000000, 59502360), strand = "+", score = 5L, GC = 0.45) ## first is within ENST0000035076 gr2 <- GRanges(seqnames = c("chr3", "chr3"), ranges = IRanges(c(58493000, 3), width=9000), strand = c("+", "-"), score = 3:4, GC = c(0.3, 0.5)) gr3 <- GRanges(seqnames = c("chr1", "chr2"), ranges = IRanges(c(1, 4), c(3, 9)), strand = c("-", "-"), score = c(6L, 2L), GC = c(0.4, 0.1)) grl <- GRangesList("gr1" = gr1, "gr2" = gr2, "gr3" = gr3) names(grl) <- c("snparray1", "snparray2", "snparray3") grl ``` The following `data.frame` matches pData sample to the `GRangesList`: ```{r} (rangemap <- data.frame(primary = c("Jack", "Jill", "Jill"), assay = c("snparray1", "snparray2", "snparray3"), stringsAsFactors = FALSE)) ``` Finally, we create a dataset of class `RangedSummarizedExperiment`: ```{r} library(SummarizedExperiment) nrows <- 5; ncols <- 4 counts <- matrix(runif(nrows * ncols, 1, 1e4), nrows) rowRanges <- GRanges(rep(c("chr1", "chr2"), c(2, nrows - 2)), IRanges(floor(runif(nrows, 1e5, 1e6)), width=100), strand=sample(c("+", "-"), nrows, TRUE), feature_id=sprintf("ID\\%03d", 1:nrows)) names(rowRanges) <- letters[1:5] colData <- DataFrame(Treatment=rep(c("ChIP", "Input"), 2), row.names= c("mysnparray1", "mysnparray2", "mysnparray3", "mysnparray4")) rse <- SummarizedExperiment(assays=SimpleList(counts=counts), rowRanges=rowRanges, colData=colData) ``` ```{r} (rangemap2 <- data.frame(primary = c("Jack", "Jill", "Bob", "Barbara"), assay = c("mysnparray1", "mysnparray2", "mysnparray3", "mysnparray4"), stringsAsFactors = FALSE)) ``` ## creating a sampleMap The `MultiAssayExperiment` constructor function can create the `sampleMap` automatically if a single naming convention is used, but in this example it cannot because we used platform-specific sample identifiers (e.g. mysnparray1, etc). So we must provide an ID map that matches the samples of each experiment back to the `pData`, as a three-column `data.frame` or `DataFrame` with three columns named "primary", "assay", and "assayname". Here we start with a list: ```{r} listmap <- list(exprmap, methylmap, micromap, rangemap, rangemap2) names(listmap) <- c("Affy", "Methyl 450k", "Mirna", "CNV gistic", "CNV gistic2") listmap ``` and use the convenience function `listToMap` to convert the list of `data.frame` objects to a valid object for the `sampleMap`: ```{r} dfmap <- listToMap(listmap) dfmap ``` Note, `dfmap` can be reverted to a list with another provided function: ```{r, eval=FALSE} mapToList(dfmap, "assayname") ``` ## Experimental data as a `list()` Create an named list of experiments for the MultiAssay function. All of these names must be found within in the third column of `dfmap`: ```{r} objlist <- list("Affy" = exprdat, "Methyl 450k" = methyldat, "Mirna" = microdat, "CNV gistic" = grl, "CNV gistic2" = rse) ``` ## Creation of the `MultiAssayExperiment` class object We recommend using the `MultiAssayExperiment()` constructor function: ```{r} myMultiAssay <- MultiAssayExperiment(objlist, patient.data, dfmap) myMultiAssay ``` The following extractor functions can be used to get extract data from the object: ```{r} Elist(myMultiAssay) pData(myMultiAssay) sampleMap(myMultiAssay) metadata(myMultiAssay) ``` Note that the `Elist` class extends the `SimpleList` class to add some validity checks specific to `MultiAssayExperiment`. It can be used like a list. ## Helper function to create a `MultiAssayExperiment` object The `PrepMultiAssay` function helps diagnose common problems when creating a `MultiAssayExperiment` object. It provides error messages and/or warnings in instances where names (either `colnames` or `Elist` element names) are inconsistent with those found in the sampleMap. Input arguments are the same as those in the `MultiAssayExperiment` (i.e., `Elist`, `pData`, `sampleMap`). The resulting output of the `PrepMultiAssay` function is a list of inputs including a "drops" element for names that were not able to be matched. Instances where `Elist` is created without names will prompt an error from `PrepMultiAssay`. Named `Elist`s are essential for checks in `MultiAssayExperiment`. ```{r} objlist3 <- objlist (names(objlist3) <- NULL) try(PrepMultiAssay(objlist3, patient.data, dfmap)$Elist) ``` Non-matching names may also be present in the `Elist` elements and the "assayname" column of the `sampleMap`. If names only differ by case and are identical and unique, names will be standardized to lower case and replaced. ```{r} names(objlist3) <- toupper(names(objlist)) names(objlist3) unique(dfmap[, "assayname"]) PrepMultiAssay(objlist3, patient.data, dfmap)$Elist ``` When `colnames` in the `Elist` cannot be matched back to the primary data (`pData`), these will be dropped and added to the drops element. ```{r} exampleMap <- sampleMap(simpleMultiAssay2) sapply(doubleExp, colnames) exampleMap PrepMultiAssay(doubleExp, patient.data, exampleMap)$drops ``` A similar operation is performed for checking "primary" sampleMap names and `pData` rownames. In this example, we add a row corresponding to "Joe" that does not have a match in the experiment data. ```{r} exMap <- rbind(dfmap, DataFrame(primary = "Joe", assay = "Joe", assayname = "New methyl")) PrepMultiAssay(objlist, patient.data, exMap)$drops ``` To create a `MultiAssayExperiment` from the results of the `PrepMultiAssay` function, take each corresponding element from the resulting list and enter them as arguments to the `MultiAssayExperiment` constructor function. ```{r} prepped <- PrepMultiAssay(objlist, patient.data, exMap) preppedMulti <- MultiAssayExperiment(prepped$Elist, prepped$pData, prepped$sampleMap) preppedMulti ``` # `RangedRaggedAssay` class Note that the GRangesList got converted to a `RangedRaggedAssay`, a class intended for data such as segmented copy number that is provides different genomic ranges for each sample. `RangedRaggedAssay` is defined by this package and inherits from `GRangesList`: ```{r} methods(class="RangedRaggedAssay") getMethod("colnames", "RangedRaggedAssay") ``` It has some additional methods that are required for any data class contained in a `MultiAssayExperiment`: ```{r} class(Elist(myMultiAssay)[[4]]) rownames(Elist(myMultiAssay)[[4]]) colnames(Elist(myMultiAssay)[[4]]) ``` One of the requirements for the `assay` method (specifically for this `RangedRaggedAssay` `Elist` element) is that the metadata have a `score` column from which to obtain values for the resulting assay matrix. Here we add ficticious values to such column contained within list elements. See `assay,RangedRaggedAssay,ANY-method` documentation. ```{r} metadata(Elist(myMultiAssay)[[4]]) <- list(snparray1 = DataFrame(score = 1), snparray2 = DataFrame(score = 1), snparray3 = DataFrame(score = 3)) assay(Elist(myMultiAssay)[[4]], background = 2) ``` # Integrated subsetting across experiments The core functionality of `MultiAssayExperiment` is to allow subsetting by assay, rownames, and colnames, across all experiments simultaneously while guaranteeing continued matching of samples. ## Subsetting samples / columns Experimental samples are stored in the rows of pData but the columns of elements of Elist, so when we refer to subsetting by columns, we are referring to columns of the experimental assays. Subsetting by samples / columns will be more obvious after recalling the pData: ```{r} pData(myMultiAssay) ``` Subsetting by samples identifies the selected samples in rows of the pData DataFrame, then selects all columns of the Elist corresponding to these rows. Here we use an integer to keep the first two rows of pData, and all experimental assays associated to those two primary samples: ```{r} subsetByColumn(myMultiAssay, 1:2) ``` Note that the above operation keeps different numbers of columns / samples from each assay, reflecting the reality that some samples may not have been assayed in all experiments, and may have replicates in some. Subsetting the primary identifiers using a character vector corresponding to some rownames of pData returns the same result: ```{r} subsetByColumn(myMultiAssay, c("Jack", "Jill")) ``` Columns can be subset using a logical: ```{r} malesMultiAssay <- subsetByColumn(myMultiAssay, pData(myMultiAssay)$sex=="M") pData(malesMultiAssay) ``` Note that selecting male patients from all assays could have been accomplished equivalently using the square bracket: ```{r} myMultiAssay[, pData(myMultiAssay)$sex=="M", ] ``` Finally, for special use cases you can exert detail control of which samples to select using a `list` or `CharacterList`, which is just a convenient form of a list containing character vectors. ```{r} allsamples <- colnames(myMultiAssay) allsamples ``` Now let's get rid of the Methyl 450k arrays 3-5, a couple different but equivalent ways: ```{r} allsamples[["Methyl 450k"]] <- allsamples[["Methyl 450k"]][-3:-5] myMultiAssay[, as.list(allsamples), ] ``` ## Subsetting assays You can select certain assays / experiments using subset, by providing a character, logical, or integer vector. An example using character: ```{r} subsetByAssay(myMultiAssay, c("Affy", "CNV gistic")) ``` Examples using logical and integer: ```{r} is.cnv = grepl("CNV", names(Elist(myMultiAssay))) is.cnv subsetByAssay(myMultiAssay, is.cnv) subsetByAssay(myMultiAssay, which(is.cnv)) ``` `subsetByRow`, `subsetByColumn`, and `subsetByAssay` are endogenous operations, in that it always returns another `MultiAssayExperiment` object. Use `assay(myMultiAssay)` to retrieve the experimental data in an ordinary `list` of datasets as their original classes. ## Subsetting rows (features) by IDs, integers, or logicals Rows of the assays correspond to assay features or measurements, such as genes. Regardless of whether the assay is ID-based (e.g. matrix, ExpressionSet) or range-based (e.g. RangedSummarizedExperiment, RangedRaggedAssay), they can be subset using any of: - a **character vector** of IDs that will be matched to rownames in each assay - an **integer vector** that will select rows of this position from each assay. This probably doesn't make sense unless every Elist element represents the same measurements in the same order and will generate an error if any of the integer elements exceeds the number of rows in any Elist element. The most likely use of integer subsetting would as a "head()" function, for example to look at the first 6 rows of each assay. - a **logical vector** that will be passed directly to the row subsetting operation for each assay. A warning is issued if this results in recycling for any of the assays. - a **list** or **CharacterList** of the same length as Elist. Each element of the subsetting list will be passed on exactly to subset rows of the corresponding element of Elist. Again, this operation always returns a `MultiAssayExperiment` class, unless "drop=TRUE" is passed to subset, with any `Elist` element not containing the feature having zero rows. For example, return a MultiAssayExperiment where `Affy` and `Methyl 450k` contain only ENST0000035076 row, and "Mirna" and "CNV gistic" have zero rows: (`drop` argument is set to `TRUE` by default) ```{r} featSubsetted0 <- subsetByRow(myMultiAssay, "ENST00000355076") class(featSubsetted0) class(Elist(featSubsetted0)) Elist(featSubsetted0) ``` In the following, `Affy` ExpressionSet keeps both rows but with their order reversed, and `Methyl 450k` keeps only its second row. ```{r} featSubsetted <- subsetByRow(myMultiAssay, c("ENST00000355076", "ENST00000294241")) exprs(Elist(myMultiAssay)[[1]]) exprs(Elist(featSubsetted)[[1]]) ``` ## Subsetting rows (features) by `GenomicRanges` For `MultiAssayExperiment` objects containing range-based objects (currently `RangedSummarizedExperiment` and `RangedRaggedAssay`), these can be subset using a `GRanges` object, for example: ```{r} gr <- GRanges(seqnames = c("chr1"), strand = c("-", "+", "-"), ranges = IRanges(start = c(1, 4, 6), width = 3)) ``` Now do the subsetting. The function doing the work here is `IRanges::subsetByOverlaps` - see its arguments for flexible types of subsetting by range. The first three arguments here are for `subset`, the rest passed on to `IRanges::subsetByOverlaps` through "...": ```{r} subsetted <- subsetByRow(myMultiAssay, gr, maxgap = 2L, type = "within") Elist(subsetted) ``` ## Subsetting by square bracket `[` The bracket method for the `MultiAssayExperiment` is equivalent but more compact than the `subsetBy*()` methods. The three positions within the bracket operator indicate rows, columns, and assays, respectively (pseudocode): ```{r, eval=FALSE} myMultiAssay[rows, columns, assays] ``` For example, to select the gene ENST00000355076: ```{r} myMultiAssay["ENST00000355076", , ] ``` The above operation works across all types of assays, whether ID-based (e.g. matrix, ExpressionSet, SummarizedExperiment) or range-based (e.g. RangedSummarizedExperiment, RangedRaggedAssay). You can subset by rows, columns, and assays in a single bracket operation, and they will be performed in that order (rows, then columns, then assays): ```{r} myMultiAssay["ENST00000355076", 1:2, c("Affy", "Methyl 450k")] ``` ## Subsetting by character, integer, and logical By columns - character, integer, and logical are all allowed, for example: ```{r} myMultiAssay[, "Jack", ] myMultiAssay[, 1, ] myMultiAssay[, c(TRUE, FALSE, FALSE, FALSE), ] ``` By assay - character, integer, and logical are allowed: ```{r} myMultiAssay[, , "Mirna"] myMultiAssay[, , 3] myMultiAssay[, , c(FALSE, FALSE, TRUE, FALSE, FALSE)] ``` ## the "drop" argument Specify `drop=FALSE` to keep assays with zero rows or zero columns, e.g.: ```{r} myMultiAssay["ENST00000355076", , , drop=FALSE] ``` Using the default `drop=TRUE`, assays with no rows or no columns are removed: ```{r} myMultiAssay["ENST00000355076", , , drop=TRUE] ``` # rownames and colnames rownames and colnames return a `CharacterList` of rownames and colnames across all the assays. A `CharacterList` is just an alternative to `list` when each element contains a character vector, that provides a nice show method: ```{r} rownames(myMultiAssay) colnames(myMultiAssay) ``` # Requirements for support of additional data classes Any data classes in the Elist object must support the following methods: * `colnames()` * `rownames()` * `[` * `dim()` Here is what happens if one of the methods doesn't: ```{r} objlist2 <- objlist objlist2[[2]] <- data.frame(objlist2[[2]]) invalid.obj <- try(MultiAssayExperiment(objlist2, patient.data, dfmap)) invalid.obj ``` # Methods for MultiAssayExperiment The following methods are defined for `MultiAssayExperiment`: ```{r} methods(class="MultiAssayExperiment") ``` # Wishlist * `c()` function for adding new assays to existing `MultiAssayExperiment` + e.g. c(myMultiAssay, neweset) + require that sample names in the new object match pData sample names + require that sample names in the new object already exist in pData * Figure out how to support a "long-and-skinny" SQL database * "mergeDups" function to merge duplicate samples in any assay + For matrix-like objects, it is clear how to do this. Default would be simple mean of the columns, but could allow user-specified functions. + For GRangesList, it's not obvious how to merge duplicates. Just concatenate? # sessionInfo() ```{r} sessionInfo() ``` [html]: http://rpubs.com/lwaldron/multiassayexperiment