Unexpected behaviour of write.csv - read.csv

-----Original Message-----
From: r-help-bounces at r-project.org 
[mailto:r-help-bounces at r-project.org] On Behalf Of Ivan Calandra
Sent: Thursday, January 13, 2011 6:44 AM
To: r-help at r-project.org
Subject: Re: [R] Unexpected behaviour of write.csv - read.csv

Hi,

I thought this was already clear from the replies to your 
previous post:
- save/load
- saveObject/loadObject from R.utils
- dput/dget (I don't remember who proposed it sorry)

There might be more possibilities, but that should do what you're 
looking for. And you should already know how each of them work and 
therefore the pros and cons.

HTH,
Ivan

Le 1/13/2011 15:08, Rainer M Krug a ?crit :

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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