Extract or subset hundreds of columns from a data frame 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 &lt;- 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.
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 &lt;- readLines("name_of_text_file")


Which returns cols as a vector of those names:

&gt; cols
[1] "GeneName1" "GeneName2"


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

mydata[ , cols]