[R] Unexpected behaviour of write.csv - read.csv

[Rainer M Krug]

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On 01/13/2011 02:56 PM, Duncan Murdoch wrote:
> On 11-01-13 6:26 AM, Rainer M Krug wrote:
> Hi
> 
> Assuming the following:
> 
>>>> x<- data.frame(a=1:10, b=runif(10))
>>>> str(x)
> 'data.frame':    10 obs. of  2 variables:
>   $ a: int  1 2 3 4 5 6 7 8 9 10
>   $ b: num  0.692 0.325 0.634 0.16 0.873 ...
>>>> write.csv(x, "x.csv")
>>>> x2<- read.csv("x.csv")
>>>> str(x2)
> 'data.frame':    10 obs. of  3 variables:
>   $ X: int  1 2 3 4 5 6 7 8 9 10
>   $ a: int  1 2 3 4 5 6 7 8 9 10
>   $ b: num  0.692 0.325 0.634 0.16 0.873 ...
>>>>
> 
> Using the two functions write.csv and read.csv, I would assume, that the
> resulting data.frame x2 be identical with x, but it has an additional
> column X, which contains the row names of x.
> 
> I know read.table and write.table which work as expected, but I would
> like to use a csv for data exchange reasons.
> 
> I know that I can use
> write.csv(x, "x.csv", row.names=FALSE)
> 
> and it would work, but shouldn't that be the default behaviour?
> 
>> I don't think so.  The CSV format is an export format which holds less
>> information than a dataframe.  By exporting the dataframe to CSV and
>> importing the result, you are discarding information and you should
>> expect to get something different.

OK - I can follow this logic - and I think I can accept it.

> 
>> If you want to save a dataframe to disk and read it back unchanged, you
>> should use save() and load().

And now my question from a previous thread (write.table equivalent for
lists?) comes up again:

using save() and load() definitely works, but it is highly unsave - as
it even keeps the names of the object, more then one can be saved, I can
not easily assign the saved object to a new name, I have problems using
the saved object if I have forgotten what the variable name was.

So I would like to expand my previous question: what are the proper
functions to store R objects? One could argue that all write...
functions are export functions - therefore keeping the data, but not
necessarily column names, rownames, attributes, ...

So what can I really do to save an R object for later usage in R?

Rainer

> 
>> Duncan Murdoch
> 
> 
> And if this is not compliant with csv files, shouldn't the function
> read.csv convert the first column into the row names?
> 
> Cheers,
> 
> Rainer
> 
>>
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- -- 
Rainer M. Krug, PhD (Conservation Ecology, SUN), MSc (Conservation
Biology, UCT), Dipl. Phys. (Germany)

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