[R] Dropping a digit with scan() on a connection

[Tim Howard]

Thank you Dr. Ripley and Christoph Buser for your explanations and
help.

Using sep = " "  within scan worked within lines of my file, but then I
gained an NA record when wrapping from one line to the next (because the
linebreak character is no longer recognized as a sep?).  So, I'll
continue by ensuring each group I read ends at the end of a line (as
scan was designed), and by using scan without the sep option.

FYI, Here's how the NA showed up, each line is 800 numbers long:

>test4 <- scan(cn.test, n=1600, sep = " ")
>test5 <- scan(cn.test, n=1600)
>test4[797:803]
[1]  81.00000  81.08746  81.89484  82.00000        NA 580.09030
576.90300
> test5[797:803]
[1]  81.01944  81.62060  81.96495  82.00000  82.00000 567.91840
563.10470

Thanks again.
Tim


>>> Prof Brian Ripley <ripley at stats.ox.ac.uk> 01/19/05 03:42AM >>>
This is because scan() has a private pushback.
Either:

1) Read the file a whole line at a time: I cannot see why you need to
do 
so here nor in your sketched application.

or

2) Use an explicit separator, e.g. " " in your example.

scan() is not designed to read parts of lines of a file,


On Tue, 18 Jan 2005, Tim Howard wrote:

> R gurus,
>
> My use of scan() seems to be dropping the first digit of sequential
> scans on a connection. It looks like it happens only within a line:
>
>> cat("TITLE extra line", "235 335 535 735", "115 135 175",
> file="ex.data", sep="\n")
>> cn.x <- file("ex.data", open="r")
>> a <- scan(cn.x, skip=1, n=2)
> Read 2 items
>> a
> [1] 235 335
>> b <- scan(cn.x, n=2)
> Read 2 items
>> b
> [1]  35 735
>> c <- scan(cn.x, n=2)
> Read 2 items
>> c
> [1] 115 135
>> d <- scan(cn.x, n=1)
> Read 1 items
>> d
> [1] 75
>>
>
> Note in b, I should get 535, not 35 as the first value. In d, I
should
> get 175.  Does anyone know how to get these digits?
>
> The reason I'm not scanning the entire file at once is that my real
> dataset is much larger than a Gig and I'll need to pull only portions
of
> the file in at once. I got readLines to work, but then I have to
figure
> out how to convert each entire line into a data.frame. Scan seems a
lot
> cleaner, with the exception of the funny character dropping issue.
>
> Thanks so much!
> Tim Howard
>
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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)
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