Unexpected behaviour of write.csv - read.csv

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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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Unexpected behaviour of write.csv - read.csv

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