Extract or subset hundreds of columns from a data frame

Question

I need to extract many columns from a dataset. 
I have a very large csv file with thousands of columns and rows, and I read it into R using:

mydata <- read.csv(file = "file.csv",header = TRUE,sep = ",",row.names = 1)

Each column is a gene name. I know how to extract specific columns from my R data.frame by using the basic code like this:

dataset[ , "GeneName1", "GeneName2"]

But my question is, how do I pull hundreds of gene names? Too many to type in? They are listed in a txt file. 
I'm new, so please go easy on jargon and abbreviations.

Jerb · Answer

Hopefully I've understood your question correctly.

Assuming your text file looks like this?

GeneName1
GeneName2

You can read that in using the readLines() function:

cols <- readLines("name_of_text_file")

Which returns cols as a vector of those names:

> cols
[1] "GeneName1" "GeneName2"

Which can then be used to subset the data frame as per your example:

mydata[ , cols]

Extract or subset hundreds of columns from a data frame

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