[BioC] how to make a specific DGEList object

[narges [guest]]

Hello
I have a counts file and I want to make a DGEList object from it.
The counts file contains the tags and all the samples of experiment(first column is for tags and other columns are the samples), but I do not want to make my object from all the samples for exapmle I need only 20 of the samples.
where can i determine it

 -- output of sessionInfo(): 

for example if i want to use the readDGE function :
d <- readDGE(myfile, , )
but i do not want all the columns from my files just some of them. how can i specify?

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