bugs in scan() (PR#304)

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Subject: bugs in scan() (PR#304)
Ray.Brownrigg@mcs.vuw.ac.nz
Date: Mon 01 Nov 1999 - 09:20:56 EST


Message-Id: <199910312320.AAA20291@pubhealth.ku.dk>

System: Sun Solaris 2.5.1

There seem to be at least 2 bugs associated with the use of flush=T in
the scan function.

1) If flush=T is used, scan() will only ask for 1 line from standard input.
Repeat by:
> R

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> scan(what=list(c1=0,c2=0,c3=0), flush=T)
1: 1 2 3 4
Read 1 lines
$c1
[1] 1

$c2
[1] 2

$c3
[1] 3

>
1a) If the 'correct' number of fields are supplied, then two lines are
read, but only 1 is 'registered':
> scan( what=list(c1=0,c2=0,c3=0),flush=T)
1: 1 2 3
1: 4 5 6
Read 1 lines
$c1
[1] 1

$c2
[1] 2

$c3
[1] 3

>

2) When reading from a file, the first line is processed correctly, but
the second and subsequent lines do not have the extraneous data flushed
correctly. Repeat by:
> write(t(matrix(1:15, ncol=5, byrow=T)), "tmp")
> system("cat tmp")
1 2 3 4 5
6 7 8 9 10
11 12 13 14 15
> scan("tmp", what=list(c1=0,c2=0,c3=0), flush=T)
Read 4 lines
$c1
[1] 1 6 10 3

$c2
[1] 2 7 11 14

$c3
[1] 3 8 12 15

Warning message:
line 3 did not have 3 elements
>
Notice that on lines 2 and 3 the first character of the "flushable
data" (after the field separator) does get flushed, but then scanning
continues. Pehaps an end-of-line indication is not reset?

Ray Brownrigg

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