[Rd] read.table messes up stdin upon small, erroneous input (PR#7722)

From: <jtk_at_cmp.uea.ac.uk>
Date: Fri 11 Mar 2005 - 13:49:08 GMT


Full_Name: Jan T. Kim
Version: 2.0.1, devel-2005-02-24
OS: Linux 2.6.x
Submission from: (NULL) (139.222.3.229)

Run read.table(stdin()) and type in the broken table 1 2
1

terminating the input by pressing Ctrl-D at the 3rd line of input. An error message by scan, complaining that "line 2 did not have 2 elements" appears, as expected. However: After this, there are three empty lines buffered in stdin:

> readLines(stdin())

[1] "" "" ""

Repeated attempts to read.table the broken input from stdin lead to even more strange results:

> read.table(stdin())

0: 1 2
1: 1
2: Error in scan(file = file, what = what, sep = sep, quote = quote, dec = dec, 
: 
        line 2 did not have 2 elements

> read.table(stdin())

3: 1 2
4: 1
[1] V1 V2
<0 rows> (or 0-length row.names)
>

Analysis: These effects are due to a combination of (1) the fact that there appear to be various routes of accessing the standard input, depending on context, and (2) the use of pushback in the process of automatically figuring out the table format:

The strange effects reported above could probably be fixed by modifying the internal readTableHead function such that it does not produce emtpy lines in order to return the number of lines "requested" by the nlines parameter.

A more fundamental approach would be to avoid pushing back lines altogether. The repeated scanning of the first few lines could be done by using a textConnection instead. Some additional work will probably be necessary to combine the first few and the remaining lines, acquired by regular operation of scan, into the complete table.



R-devel@stat.math.ethz.ch mailing list
https://stat.ethz.ch/mailman/listinfo/r-devel Received on Mon Mar 14 09:57:34 2005

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