[R] How to import specific column(s) using "read.table"?

[Liaw, Andy]

Use as.list.

Andy

> From: F Duan
> 
> Thanks a lot. 
> 
> Your way works perfect. And one more tiny question related to 
> your codes:
> 
> My data file has many columns to be omitted (suppose the 
> first 20 ones), but I 
> found "scan(myfile, what=list(rep(NULL, 20), rep(0, 5))" 
> doesn't work. I had to 
> to type "NULL" 20 times and "0" five times in the "list(...)". 
> 
> But anyway, it works and saves a lot of memory for me. Thank 
> you again.
> 
> Frank 
> 
> 
> Quoting Gabor Grothendieck <ggrothendieck at myway.com>:
> 
> > Gabor Grothendieck <ggrothendieck <at> myway.com> writes:
> > 
> > : 
> > : F Duan <f.duan <at> yale.edu> writes:
> > : 
> > : > I have a very big tab-delim txt file with header and I 
> only want to
> > import 
> > : > several columns into R. I checked the options for 
> Â"read.tableÂ" and only
> > 
> > : 
> > : Try using scan with the what=list(...) and flush=TRUE arguments.  
> > : For example, if your data looks like this:
> > : 
> > : 1 2 3 4 
> > : 5 6 7 8 
> > : 9 10 11 12
> > : 13 14 15 16
> > : 
> > : then you could read columns 2 and 4 into a list with:
> > : 
> > 
> > oops. That should be 1 and 3.
> > 
> > :    scan(myfile, what = list(0, NULL, 0), flush = TRUE)
> > : 
> > : or read in and convert to a data frame via:
> > : 
> > :    do.call("cbind", scan(myfile, what = list(0, NULL, 0), 
> flush = TRUE))
> > 
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