[R] skipping columns with read.fwf?
asone at latte.harvard.edu
Sat May 4 05:43:59 CEST 2002
While at least two people had already responded to your question and
probably you may have received other tips on this topic personally, this
e-mail intends to have two of these other tips get into the help archive
for future reference.
1. cut command and read.fwf
This is a once-and-for-all (preprocessing the file before R) approach:
if you handle the file on some Linux/Unix-type platform, you can extract
the necessary columns from the data file and save them as a new file by
using 'cut' command with -b option and '> a_new_file_name' [redirection]
; for MS windows, cut.exe can be found within the tools.zip available at
2. customize read.fwf
As Professor Ripley mentioned in his e-mail, read.fwf isn't suitable for
large files; however, if you stick to solutions within R, one approach
is to customize read.fwf that is just a wrapping function of scan,
read.table, and others. As you can see, read.fwf internally calculates
first and last positions to cut/save relevant columns [i.e., an internal
function, doone]; therefore, instead of the argument widths, these
first/last positions can be externally given to the function as new
argument(s) of your customized read.fwf.
Harvard-MIT data center
> -----Original Message-----
> From: owner-r-help at stat.math.ethz.ch
> [mailto:owner-r-help at stat.math.ethz.ch] On Behalf Of Brett A Magill
> Sent: Friday, May 03, 2002 12:54 PM
> To: r-help at stat.math.ethz.ch
> Subject: [R] skipping columns with read.fwf?
> I have a file in fwf. It is rather large, about 40,000 rows
> and 40 variables (columns). I only need about 10 variables
> form the data set for the analysis at hand. Unfortunately,
> these 10 variables are not contiguous in the file, for
> example, the first is position 1-8, the next position 25-27, then 40.
> Is there a way to read the selected varaibles that I need
> without reading in the entire data set?
> r-help mailing list -- Read
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