[BioC] How to look at the output of the Poisson data model
Mark Robinson
mrobinson at wehi.EDU.AU
Thu Oct 2 11:32:05 CEST 2008
Hi Milena.
Thank you for your comments. I had originally added the Poisson special
case as somewhat of an afterthought. But, it appears that it is
worthwhile to have it covered by the 'deDGE' command itself. So, ...
I've made the following changes:
1. In the 'deDGE' command, there is now an argument 'doPoisson', which
when set to TRUE skips the dispersion moderation step, but still
calculates the 'exact' test on the quantile-adjusted data. So, the
Poisson analysis returns an object of the correct type for 'topTags'.
2. I've added a 'plotMA' method for 'deDGEList' objects, similar to
limma's ... it saves some of the mucking about forming M and A that was
previously done by hand.
3. Vignette updated.
Sorry I hadn't thought of doing this sooner!
Cheers,
Mark
> Dear Mark (and edgeR users),
>
> Thanks so much for your feedback. That solved the problem and also was
> good advice regarding the low tag counts.
>
> I am facing another obstacle:
> I tried fitting the Poisson model instead of the negative binomial. The
> MAplot and boxplots from this method look good.
> Now my problem is, how do I get a table with the resulting
> differentially expressed tags of out of the Poisson model?
> topTags() does not work on the object resulting from exactTestNB(),
> because it is not a deDGEList...
>
> My full code is below.
> Thanks again!
>
> #-----------------------
>
> d <- new("DGEList", list(data=as.matrix(mydata), group=grouping,
> lib.size=lib_size))
> d
> head(d$data)
> A.REP1 A.REP2 B.REP1 B.REP2
> 100168004_100169791_- 2 4 3 1
> 100175732_100176961_- 0 3 2 3
> 100471575_100982094_- 0 0 0 4
> 101147427_101152326_- 1 0 0 4
> 101147433_101152326_- 3 1 1 2
> 101152469_101153215_- 4 21 8 46
>
> qA <- quantileAdjust(d, r.init=1000, n.iter=1)
>
> par(mfrow=c(1,2))
> boxplot(as.data.frame(sqrt(d$data)))
> boxplot(as.data.frame(sqrt(qA$pseudo)))
>
> f <- exactTestNB(qA$pseudo, d$group, qA$N * qA$ps$p, r=1000)
>
> #------------------------
>
> Mark Robinson wrote:
>> Hi Milena.
>>
>> Small oversight on my part. If you use 'as.matrix(mydata)' in place of
>> 'mydata', you should have no problems. This is imposed on the data
>> matrix
>> in the next version (which might take a day or so to come online).
>>
>> A couple of other small points:
>>
>> 1. You may want to use the new constructor (instead of creating the list
>> yourself):
>>
>> d<-DGEList(data=y,group=grouping,lib.size=lib_size)
>>
>> 2. In terms of analysis of differential expression, there may not be
>> much
>> value in the rows of your table that have VERY low counts (e.g. your
>> 100134814_100136947). In the past, I've noticed some instabilities in
>> the
>> NB calculations with very low counts and I've generally filtered out the
>> rows with (say) 3 or less total counts.
>>
>> Cheers,
>> Mark
>>
>>
>>
>>
>>> Dear edgeR developers and users,
>>>
>>> Just started using edgeR with next generation sequence (count) data.
>>> When calculating alpha, I am getting the following error:
>>>
>>> alpha <- alpha.approxeb(d)
>>> [quantileAdjust] Iteration (dot=1000) 1 :Error in y1/matrix(rep(1,
>>> nrow(y1)), ncol = 1) %*% lib.size1 :
>>> non-numeric argument to binary operator
>>>
>>> I can't work out why I am getting this... any ideas?
>>> Thanks!
>>>
>>> The full code is below:
>>> --------------
>>> mydata <- read.table("myFile.txt", header=TRUE, row.names="ID")
>>> head(mydata)
>>> A.REP1 A.REP2 B.REP1 B.REP2
>>> 100011872_100012727_- 0 0 0 2
>>> 100017569_100017878_- 1 0 0 0
>>> 100134814_100136947_- 0 0 0 0
>>> 100134931_100136947_- 0 2 0 0
>>> 100137054_100138100_- 1 0 0 1
>>> 100137831_100138100_- 1 0 0 0
>>>
>>> grouping <- c(1,1,2,2)
>>> lib_size <- as.numeric(apply(mydata,2,sum))
>>> lib_size
>>> [1] 352812 573571 401573 719698
>>>
>>> d <- new("DGEList", list(data=mydata, group=grouping,
>>> lib.size=lib_size))
>>> alpha <- alpha.approxeb(d)
>>> [quantileAdjust] Iteration (dot=1000) 1 :Error in y1/matrix(rep(1,
>>> nrow(y1)), ncol = 1) %*% lib.size1 :
>>> non-numeric argument to binary operator
>>> ---------------------
>>>
>>> --
>>> Milena
>>>
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>>>
> Milena
>
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