R help - Oct 2001 - File reading.

Hi all,

Appologies for the rather basic IO question but I am rather new to R...
Migrated from IDL/Matlab recently.  I have a rather simple Fortran
control file (sigh...) that I am trying to parse and read using R.  My
problem is that the file's format is somewhat flexible.  Imagine:

---
1>  39 1901
2>  1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
3>   22 24 26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 56 58
4>     650.0   650.5   651.0   651.5   652.0   652.5   653.0   653.5   654.0
5>     654.5   655.0   655.5   656.0   656.5   657.0   657.5   658.0   658.5
         ...
7>    1599.5  1600.0
8>
9>  1 1 0
10> Xtemp.wf
11> 2
12> Xtemp.noise
13> 4
14> Xtemp.Sa
---

Line 1 contains 2 numbers (nx, ny) which can easily be read using scan.
If nx>0 then there are nx values to be read next (i.e. lines 2 and 3 have
39 values).  Likewise, with ny>0, lines 4-7 give 1901 values.  However, if
nx or ny are less than 0, then the data block for lines 2-3 or lines 4-7
will not be present and a generic index is made...  In psudo code:

---
# get the file handle for the case file
fin=fopen(casefile);

# read the file
in=fscanf(fin,'%f',2);

# first 2 numbers in the case file give the size
nx=in(1);
ny=in(2);

# read or construct the x label
if nx>0
    xlab=fscanf(fin,'%f',nx);
else
    nx=-nx;
    xlab=0:(nx-1);
end

# read or construct the y label
if ny>0
    ylab=fscanf(fin,'%f',ny);
else
    ny=-ny;
    ylab=1:ny;
end
---

My problems are that R seems to be tied to the line numbers on which data
is found and that the scan function doesn't remember where it last was...
Is there some C-like fopen/fread construct that I am missing?

Cheers,
Randall

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On Wed, 17 Oct 2001, Randall Skelton wrote:
> Hi all,
> 
> Appologies for the rather basic IO question but I am rather new to R...
> Migrated from IDL/Matlab recently.  I have a rather simple Fortran
> control file (sigh...) that I am trying to parse and read using R.  My
> problem is that the file's format is somewhat flexible.  Imagine:
> 
> ---
> 1>  39 1901
> 2>  1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
> 3>   22 24 26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 56 58
> 4>     650.0   650.5   651.0   651.5   652.0   652.5   653.0   653.5  
654.0
> 5>     654.5   655.0   655.5   656.0   656.5   657.0   657.5   658.0  
658.5
>          ...
> 7>    1599.5  1600.0
> 8>
> 9>  1 1 0
> 10> Xtemp.wf
> 11> 2
> 12> Xtemp.noise
> 13> 4
> 14> Xtemp.Sa
> ---
> 
> Line 1 contains 2 numbers (nx, ny) which can easily be read using scan.
> If nx>0 then there are nx values to be read next (i.e. lines 2 and 3
have
> 39 values).  Likewise, with ny>0, lines 4-7 give 1901 values.  However,
if
> nx or ny are less than 0, then the data block for lines 2-3 or lines 4-7
> will not be present and a generic index is made...  In psudo code:
> 
> ---
> # get the file handle for the case file
> fin=fopen(casefile);
> 
> # read the file
> in=fscanf(fin,'%f',2);
> 
> # first 2 numbers in the case file give the size
> nx=in(1);
> ny=in(2);
> 
> # read or construct the x label
> if nx>0
>     xlab=fscanf(fin,'%f',nx);
> else
>     nx=-nx;
>     xlab=0:(nx-1);
> end
> 
> # read or construct the y label
> if ny>0
>     ylab=fscanf(fin,'%f',ny);
> else
>     ny=-ny;
>     ylab=1:ny;
> end
> ---
> 
> My problems are that R seems to be tied to the line numbers on which data
> is found and that the scan function doesn't remember where it last
was...
> Is there some C-like fopen/fread construct that I am missing?
> 
Maybe try file(), open(), and readLines(), see Brian Ripley's introduction
to using connections in R-News number 1, pages 16-17.

Roger

-- 
Roger Bivand
Economic Geography Section, Department of Economics, Norwegian School of
Economics and Business Administration, Breiviksveien 40, N-5045 Bergen,
Norway. voice: +47 55 95 93 55; fax +47 55 95 93 93
e-mail: Roger.Bivand at nhh.no
and: Department of Geography and Regional Development, University of
Gdansk, al. Mar. J. Pilsudskiego 46, PL-81 378 Gdynia, Poland.

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Laurent Gautier			CBS, Building 208, DTU
PhD. Student			D-2800 Lyngby,Denmark	
tel: +45 45 25 24 85		http://www.cbs.dtu.dk/laurent

On Wed, 17 Oct 2001, Randall Skelton wrote:
> My problems are that R seems to be tied to the line numbers on which data
> is found and that the scan function doesn't remember where it last
was...
> Is there some C-like fopen/fread construct that I am missing?

The use of connections could be something worth being tried.

The command 'readLines' reads lines from a connection (and in this sense
'remembers' where it last was...)

try 

help(file)
help(readLines)


Hopin' it helps,



Laurent

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(in the "body", not the subject !)  To: r-help-request at
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