Question: How to combine count matrix with mouse gene information from Ensemble using Biomart in R
gravatar for lamia_203
5 months ago by
lamia_20330 wrote:


I am trying to add a row of gene id next to my rows of gene symbols. normlaised_mouse3 is my count matrix for rna-seq analysis. I've used to code:

normalised_mouse_biomart <- read.delim("normalised_mouse3.txt")
mart <- useDataset("mmusculus_gene_ensembl", useMart("ensembl"))
Genes <- normalised_mouse_biomart$V2
ensLookup <- gsub("\\.[0-9]*$", "", Genes)
G_list <- getBM(filters= "ensembl_gene_id", 
                attributes= c("ensembl_gene_id" , "mgi_symbol"),
                values= ensLookup,
                mart= mart)
mouse <- cbind(G_list$mgi_symbol, normalised_mouse_biomart)

G_list contains the correct list of gene id and gene symbol but there are error messages when merging the gene ID and count matrix:

Error in data.frame(..., check.names = FALSE) : 
  arguments imply differing number of rows: 54439, 54446

I don't understand how 7 gene names are missing from the G_list when I've given the correct number of gene symbols.

R rna-seq biomart ensembl • 315 views
ADD COMMENTlink modified 5 months ago by zx87547.9k • written 5 months ago by lamia_20330

Well for starters, how many genes are in ensLookup? How many unique genes in G_list? Is there any possibility that the gsub is mangling a few gene names?

ADD REPLYlink written 5 months ago by swbarnes26.1k

If you want to store meta-data for your genes alongside read-counts for those features in your samples, you might be better storing your data in a edgeR::DGEList.

ADD REPLYlink written 5 months ago by russhh4.6k
gravatar for Kevin Blighe
5 months ago by
Kevin Blighe46k
Kevin Blighe46k wrote:


I would not do this:

cbind(G_list$mgi_symbol, normalised_mouse_biomart)

Why? - biomaRt will not return the data in the same order as it was submitted. It will neither, most likely, be able to map all genes. It follows, too, that biomaRt may annotate one of your genes multiple times.

You should always check the contents of your objects before performing operations on them. In programming, expect the unexpected.

You can use a combination of !duplicated(), match(), and which() for the purposes of re-ordering the biomaRt return object so that it is harmonised with your input data.


ADD COMMENTlink written 5 months ago by Kevin Blighe46k
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