Simple Affy Differential Expression

Question

I think I have a fairly easy-to-solve problem.

I have an expression table generated from an Affy set. It has one row of gene names (already symbols) and then 180 sample rows. 181 rows total.

So I made another excel file with one row with three different phenotypes I want to compare. That row has a label ("classes") and 180 names. 181 rows total.

In R, I can import each of these

dat <- read.csv("expression.csv")
dat <- data.matrix(dat)
pheno <- read.csv("pheno.csv")
pheno <- data.matrix(pheno)

I can then fit them

fit <- lmFit(dat,pheno)

And ask for an eBayes from limma

fit <- eBayes(fit)

Now, when I view the topTable,

table <- topTable(fit)

My first column has numbers (like "834","1142"), when I'd expect to have gene names there (like "ACTR", "CHRNA1").

What am I doing wrong? Or, rather, am I doing anything right?

Thanks!

Answer 1

What do the first few lines of your lmFit input variables look like (i.e. dat and pheno)? Are the rows numbered, or do they use the actual symbols?

By default, I don't think read.csv expects a file to have row numbers (even though write.csv puts them in by default). Try adding a row.names parameter to the expression matrix read call:

dat <- read.csv("expression.csv", row.names=1)