[R] How to convert "c:\a\b" to "c:/a/b"?

[(Ted Harding)]

On 27-Jun-05 Spencer Graves wrote:
>         Thanks, Dirk, Gabor, Eric:
> 
>         You all provided appropriate solutions for the stated problem. 
> Sadly, I oversimplified the problem I was trying to solve:  I copy a 
> character string giving a DOS path from MS Windows Explorer into an R 
> script file, and I get something like the following:
> 
>         D:\spencerg\statmtds\R\Rnews
> 
>         I want to be able to use this in R with its non-R meaning,
e.g., in 
> readLine, count.fields, read.table, etc., after appending a file name. 
> Your three solutions all work for my oversimplified toy example but are
> inadequate for the problem I really want to solve.

The various responses show that solving this problem directly within
R may be, well, problematic!

I'm not a perl user, but possibly Spencer Graves's speculation might
eventually be brought into a straightforward solution.

Unfortunately, for this query, I'm not a Windows users either, so
can't be authoritative about how practical the following may be for
Spencer's problem (and similar).

In the Unix world, the "string editor" program 'sed' simply mops
up problems of this kind. For example, I just did:

  echo "D:\spencerg\statmtds\R\Rnews" | sed 's@\\@/@g'

and got the response:

  D:/spencerg/statmtds/R/Rnews

Note: the parsing of the 'sed' command is as follows:

  s at x@y at g means substitute "y" for every ("g" = "global") occurrence
          of "x".

  The character to be replaced (x="\") is the escape character so
  needs to be escaped ("\\"); but apart from this it's straightforward.

  The usual separator is "/" instead of "@", but I used "@"
  to simplify things since the substitute itself is y="/".

  An alternative using "/" as separator would be

    echo "D:\spencerg\statmtds\R\Rnews" | sed 's/\\/\//g'
    D:/spencerg/statmtds/R/Rnews

  which is a bit more complicated but still straightforward
  (depending on your eyesight). Here, both x="\" and y="/"
  need to be escaped.

'sed', and a lot of other useful stuff, is available as "GNU tools"
which can be installed on Windows, and allow this kind of thing to
be very slickly done, but outside of R of course.

I also make much use of 'awk' (but you can equally use perl) for
tidying up CSV files exported from Excel, and for all sorts of
rearrangements and substitutions in data files. While Unix users
take this sort of thing for granted, I suggest to Windows users
that it could be well worth installing the GNU tools, since they
are very useful indeed.

It's not clear from Spencer's follow-up whether doing this kind
of preliminary work outside of R, and then bringing the results
into R (e.g. via the clipboard or a file) is practical in his
context. If not (i.e. all the work has to be done inside R), then
of course my sugestion above is not helpful in this case!

Best wishes,
Ted.


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Date: 28-Jun-05                                       Time: 13:38:37
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