[R] Reading from files

[Prof Brian Ripley]

To read just one row it is easier to use scan() directly (it lies
underneath read.table)

scan("foo", list(num=0, a="", b="", c=""), nmax=1, sep =",")
$num
[1] 1000
$a
[1] "x"
$b
[1] "y"
$c
[1] "z"

gives the four items in a list.

I didn't see why you would want to read just one line.  If you are doing
this repeatedly it is normally better to use read.csv to read the whole
file and process all the rows at once in R.


On Wed, 1 May 2002, Marc Schwartz wrote:

> > Hi,
> >
> > I am a novice to R and have a question here. Is it possible to read a
> > single line from a file into a vector or list etc? If so, is it
> possible
> > to read comma separated values?
> > Eg:
> > 1000,x,y,z
> > 1001,s,d,f
> >
> > How do I read the first line only i.e. 1000,x,y,z from the file and
> that
> > too so that I get separate storage for 1000, x, y and z?
> >
> > Thanks in advance.
> > Saket.
>
> Review the "nrows" option for the read.csv function (?read.csv).  It
> lets you specify how many rows to read from a delimited file.  In the
> help file the option is listed for read.table, but it applies to
> read.csv as well. The differences between the variations of read.* are
> the default values.
>
> For read.csv, the default value for nrows is -1, which reads in all
> rows. The default delimiter for read.csv is ",". Also, the default value
> for the "header" option is TRUE, which indicates that the first row in
> your file contains column names. If your data is structured as you
> define above, set header = FALSE.
>
> Thus, to read in the first line only, add in "nrows = 1" to the
> arguments, such that the command would be:
>
> > V <- read.csv(FileName, nrows = 1, header = FALSE, ....)
>
> Note that the option "skip = x" lets you tell the function to skip a
> certain number of rows before starting the read.
>
> The combination of skip and nrows let's you read in a specific subset of
> rows from a larger file.  For example to read in rows 6 through 10, you
> would use:
>
> > V <- read.csv(FileName, skip = 5, nrows = 5, header = FALSE, ...)
>
> Hope that helps.
>
> Marc Schwartz
>
>
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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 272860 (secr)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595


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