[R] Skipping specified rows in scan or read.table

[Prof Brian Ripley]

On Wed, 9 Apr 2008, Ravi Varadhan wrote:

> Hi,
>
>
>
> I have a data file, certain lines of which are character fields.  I would
> like to skip these rows, and read the data file as a numeric data frame.  I
> know that I can skip lines at the beginning with read.table and scan, but is
> there a way to skip a specified sequence of lines (e.g., 1, 2, 10, 11, 19,
> 20, 28, 29, etc.) ?

Not within scan, but you can do it within the connection that scan reads.

If the file is small, just read it all with readLines, select the lines 
you want (mydata[-c(1,2,10,11...)]) and use that as the input to a 
textConnection.  If it is large, read a line at a time, discard when it is 
one to be skipped otherwise write to an anonymous file() connection.  Then 
read.table on the anonymous connection.

Or use perl/awk within a pipe() connection.

> If I read the entire data file, and then delete the character fields, the
> values are still kept as factors, with each value denoted by its level.
> Since, I have continuous variables, there are as many levels as there are
> values.  I am unable to coerce this to "numeric" mode.  Is there a way to do
> this so that I can then manipulate the numeric data frame?

Why does FAQ Q7.10 not apply?

>
>
>
> Thanks for any help.
>
> Best,
>
> Ravi.
>
> ----------------------------------------------------------------------------
> -------
>
> Ravi Varadhan, Ph.D.
>
> Assistant Professor, The Center on Aging and Health
>
> Division of Geriatric Medicine and Gerontology
>
> Johns Hopkins University
>
> Ph: (410) 502-2619
>
> Fax: (410) 614-9625
>
> Email: rvaradhan at jhmi.edu
>
> Webpage:  http://www.jhsph.edu/agingandhealth/People/Faculty/Varadhan.html
>
>
>
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>
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-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595