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

[Barry Rowlingson]

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
>
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