[R] Scanning data files line-by-line

[Spencer Graves]

With a "connection" instead of a "file", there is no counterpart to 
"count.fields" to summarize what's available?

Thanks,
Spencer Graves

Prof Brian Ripley wrote:
> On Wed, 30 Apr 2003, R A F wrote:
> 
> 
>>Thanks very much.  I guess the answer leads to more questions:
>>
>>(a) What if I don't know the number of lines?  So I would like to use
>>    a while loop until readLines hits an EOF character.  Would that
>>    be possible?
> 
> 
> Yes. After you reach the end of the file you will get character(0) since
> 
> Value:
> 
>      A character vector of length the number of lines read.
> 
> and zero lines would have been read.
> 
> 
>>(b) When readLines is used, a string is returned.  
> 
> 
> Not quite: a character vector is returned.
> 
> 
>>I'd like to split
>>    the string into fields, and Andy Liaw suggested strsplit, but the
>>    number of spaces between fields is variable.  So for example, one
>>    line could be 1 space 2 space space 3 and the next line could be
>>    4 space space 5 space 6, so I could not do a strsplit using " ".
>>
>>    Really what I know is the variable type of each field -- for
>>    example, each line is double, string, then double, etc.  How
>>    would one use this information to split the string given by
>>    readLines?
> 
> 
> You could use scan on the line: it works on textConnections.
> 
> 
>>Thanks very much again!
>>
>>
>>>From: Prof Brian Ripley <ripley at stats.ox.ac.uk>
>>>To: R A F <raf1729 at hotmail.com>
>>>CC: R-help at stat.math.ethz.ch
>>>Subject: Re: [R] Scanning data files line-by-line
>>>Date: Wed, 30 Apr 2003 14:13:26 +0100 (BST)
>>>
>>>It's open() you need, as in
>>>
>>>con <- file("file")
>>>open(con)
>>>for(i in 1:10) print(readLines(con, n=1))
>>>close(con)
>>>
>>>In C you would need to (f)open a file to read it line-by-line, just as
>>>here.
>>>
>>>The first two lines can be collapsed to
>>>
>>>con <- file("file", "r")
>>
>>
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