[R] How to reach the column names in a huge .RData file without loading it

[Richard M. Heiberger]

Barry's solution works with Windows without cygwin.
You do need Rtools, available from the Windows page on CRAN

Rtools does not have "gunzip", but that is just an abbreviation for "gzip -d".

x:\HOME\rmh\HH-R.package>path
path
PATH=c:\Progra~2\Rtools\bin;c:\Progra~2\Rtools\gcc-4.6.3\bin;c:\progra~1\R\R-3.2.3\bin\x64;c:\Progra~1\MikTeX~1.9\miktex\bin\x64;c:\windows;c:\windows\system32

x:\HOME\rmh\HH-R.package>gzip -d -c
c:\Users\rmh.DESKTOP-60G4CCO\test.RData | strings -t d
gzip -d -c c:\Users\rmh.DESKTOP-60G4CCO\test.RData | strings -t d
      0 RDX2
     35 mydataframe
    230 names
    251 mylongnamehere
    273 anotherlongname
    314 aasdkjhasdkjhaskdj
    347 row.names
    389 class
    410 data.frame

On Wed, Mar 16, 2016 at 1:17 PM, Barry Rowlingson
<b.rowlingson at lancaster.ac.uk> wrote:
> You *might* be able to get them from the raw file...
>
> First, I don't quite know what "colnames" of an .RData file means.
> "colnames" are the column names of a matrix (or data frame), so I'll
> assume your .RData file contains exactly one data frame and you want
> to column names of it.
>
> So let's create one of those:
>
>
> mydataframe = data.frame(mylongnamehere=runif(3),
> anotherlongname=runif(3), z=runif(3), y=runif(3),
> aasdkjhasdkjhaskdj=runif(3))
> save(mydataframe, file="./test.RData")
>
> Now I'm going to use some Unix utilities to see if there's any
> identifiable strings in the file. .RData files are by default
> compressed using `gzip`, so I'll `gunzip` them and pipe it into
> `strings`:
>
> $ gunzip -c test.RData | strings -t d
>       0 RDX2
>      35 mydataframe
>     230 names
>     251 mylongnamehere
>     273 anotherlongname
>     314 aasdkjhasdkjhaskdj
>     347     row.names
>     389 class
>     410 data.frame
>
>
>   - thats found the object name (mydataframe) and most of the column
> names except the short ones, which are too short for `strings` to
> recognise. But if your names are long enough (4 or more chars, I
> think) they'll show up.
>
>  Of course you'll have to filter them out from all the other string
> output, but they should all appear shortly after the word "names",
> since the colnames of a data frame are the "names" attribute of the
> data.
>
>  If you don't have a Unix or Mac machine handy you can get these
> utilities on Windows via Cygwin but that's another story...
>
>  Barry
>
>
>
>
>
>
>
>
> On Wed, Mar 16, 2016 at 3:59 PM, Lida Zeighami <lid.zigh at gmail.com> wrote:
>> Hi,
>> I have a huge .RData file and I need just to get the colnames of it. so is
>> there any way to reach the column names without loading or reading the
>> whole file?
>> Since the file is so big and I need to repeat this process several times,
>> so it takes so long to load the file first and then take the colnames!
>>
>> Thanks
>>
>>         [[alternative HTML version deleted]]
>>
>> ______________________________________________
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>> and provide commented, minimal, self-contained, reproducible code.
>
> ______________________________________________
> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.