[R] Problem passing data into read.table()

[David R. McWillliams]

I thought about scan(), but I think that would require knowing the number
of columns beforehand.  As I noted before, if I put in the number of
rows in the second call to read.table(), say 'nrows=2000', it correctly
detects the number of columns and rows.  I just can't get it to see the
calculated value as in 'nrows=row.ctr'.  The intervening print() can fetch
the value of row.ctr, so I don't understand why read.table() can't get it.



On Mon, 22 Apr 2002, Huntsinger, Reid wrote:

>Date: Mon, 22 Apr 2002 15:02:31 -0400
>From: "Huntsinger, Reid" <reid_huntsinger at merck.com>
>To: 'David R. McWillliams' <dmcwilli at utk.edu>, r-help at stat.math.ethz.ch
>Subject: RE: [R] Problem passing data into read.table()
>
>I think you should avoid read.table here. It tries to set various parameters
>(number of columns, etc) by looking at a part of your file. Even if you
>specify col.names, it can get confused by this looking-ahead. Better look at
>the definition of read.table in terms of scan and readLines and modify to
>your needs.
>
>Perhaps your problem isn't that nrows doesn't get the right value, but that
>read.table is using the wrong number of columns. (Actually, I can't create
>an example like yours that read.table doesn't complain about line 1 not
>having n elements, where n is the number of elements in the longest line.)
>
>If you really want to make read.table work, you can probably use the
>fill=TRUE option and lots of caution.
>
>Reid Huntsinger
>
>-----Original Message-----
>From: David R. McWillliams [mailto:dmcwilli at utk.edu]
>Sent: Monday, April 22, 2002 1:13 PM
>To: r-help at stat.math.ethz.ch
>Subject: [R] Problem passing data into read.table()
>
>
>I am trying to read in a tab-delimited data file with a 21 row header and
>2 row footer using two calls to read.table().  Numbers of rows and columns
>are variable.  The header contains information for calculating the number
>of rows of data.  I can successfully pick this out and calculate the
>number of rows to read, but cannot get the second read.table() to assign
>this number to "nrows"  (the number is correct; if I enter it manually,
>the everything works fine).  Currently the function reads all the way to
>the end and crashes on the footer, since the number of fields is different
>from that of the data.
>
>I know this could easily be done with some Perl pre-processing of the
>file, but it is going to run on a Windows machine and I am trying to
>minimize the number of packages to download.  Nevertheless, there is the
>general problem of why I cannnot pass a calculated value into the 
>function.
>
>Code follows.
>
>#
># function to read data with header and footer
>#
>
># pick line 8 with the data layout information and calculate the number of
>rows ...
>grid.layout <- read.table(fname, as.is=T, header=F, sep="\t",
>comment.char="", skip=7, nrows=1)
>row.ctr <- grid.layout[4]*grid.layout[5]*grid.layout[6]*grid.layout[7]
>
># tells me I have the right dimensions ...
>print(row.ctr)
>
># but they do not get passed into this read.table() ...
>tmp.df <- read.table(fname, as.is=T, header=T, sep="\t", comment.char="",
>skip=20, nrows=row.ctr )
>tmp.df
>
># end function
>
>
>Regards,
>
>
>
>David R. McWilliams
>dmcwilli at utk.edu
>
>
>
>
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David R. McWilliams
dmcwilli at utk.edu


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