Hi!!

I'm having trouble to do a contrast using DESeq2. I have 12 samples, AA(2 replicates), AB(4 replicates), BA(4 replicates) and BB(2 replicates). I wanted to compare AB (or BA) with the mean of AA and BB, so I found out that I should do this from another post:

res <- results(dds, contrast=list("conditionAB", c("conditionAA", "conditionBB"), listValues=c(1, -1/2))

But I couldn't get it work. The error says conditionAA, conditionBB etc are not in resultNames().

Here is my code:

countData <- read.csv(file = dataFile, header = TRUE,  row.names=1)
colData <- DataFrame(row.names=colnames(countData), condition=factor(c(rep("AA",2), rep("AB",4), rep("BA",4), rep("AA",2))))

dds <- DESeqDataSetFromMatrix(countData = countData,

                                colData = colData,
                                design = ~condition)
 

dds <- DESeq(dds)

res <- results(dds, contrast=list("conditionAB", c("conditionAA", "conditionBB"), listValues=c(1, -1/2))

When I check resultsNames(dds), I got those:

[1] "Intercept"          "condition_AB_vs_AA" "condition_BA_vs_AA" "condition_BB_vs_AA"

I would like to have "conditionAA", "conditionBB" etc. in the resultsNames() output, so I can make the contrast I mentioned. I have been reading on this website for hours but couldn't find the solution. Any suggestions would be highly appreciated!

Thank you!

-Zhu

You can have design = ~condition-1 to remove the intercept terms, or you can alter the formulation of the contrast using the existing names by using the fact that Intercept is really conditionAA, and so conditionBB is Intercept+conditionBB_vs_AA etc, and doing the algebra to get your numerators and denominators in terms of the existing resultsNames.  I get contrast=list("condition_AB_vs_AA", "condition_BB_vs_AA") with listVars=c(1,-1/2), but you might want to double-check that!