The issue is the pushback on text files (which readChar does not use). I've altered the logic in 2.7.2 patched so that seek() clears the pushback. NB: 1) Your code is incomplete (you need library(MASS)), 2) You are asked not to report on obsolete versions of R.
On Sat, 30 Aug 2008, alex at apeironsports.com wrote:
Full_Name: Dr. Alex Sheppard Version: 2.7.1 OS: Linux Debian Lenny Submission from: (NULL) (79.73.224.62) After scanning from an open (text) connection, then seeking, then scanning again, the second scan returns incorrect result. It looks like the first byte scanned was from the pre-seek file position, then it continues to read from the post-seek file position. To reproduce: #Put 3x3 matrix in a file
write.matrix(t(matrix(1:9,nrow=3)),file="TEST.txt",sep="\t")
#Open file as text
fd <- file("TEST.txt",open="rt")
#scan a couple of fields - this looks fine so far
scan(file=fd,what=double(),n=2)
Read 2 items [1] 1 2 #seek back to start of file
seek(con=fd,where=0,origin="start")
[1] 5 #scan fields again - this doesn't work properly
scan(file=fd,what=double(),n=2)
Read 2 items
[1] 31 2
This happens when either n or nmax arguments are used to control number of
fields read. Problem does not occur when using nlines argument instead. The seek
appears to work ok, as doing readChar(fd,n=1) after the seek operation correctly
returns "1".
Also, if the file is opened as binary, i.e. fd=file("TEST.txt",open="rb") , all
works fine.
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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