[R] RODBC to import/export xls files

[Ivan Calandra]

Dear R users,

I've learned today about RODBC package in order to import xls file to 
dataframes and export the dataframes to xls files.

However I have some problems. Please excuse me if these are basic but as 
I said, I've just begun with this package.
Also this email is quite long, but everything is related, so I don't 
think it would be better to split it. Moreover, there's a lot from an 
error message and dput(). I hope it won't discourage you. I believe I've 
compressed it as much as possible

- to import, I do this:
con <- odbcConnectExcel("D:\\R\\cdeg_SSFA_R.xls")
cdeg <- sqlFetch(con, "cdeg")
close(con)
It works great, but is there a way without giving the sheet name (here 
"cdeg")?
The thing is that I almost always have a single sheet in my xls files, 
which is not really named (usually sheet1, sheet2, etc), so it would be 
great if I could just import the 1st sheet into the dataframe.

- to export I do this (from Tal Galili's solution earlier today):
xlsFile <- odbcConnectExcel("file", readOnly=F)
save2excel <- function(x, t.name) sqlSave(xlsFile, x, tablename=t.name, 
rownames=F, addPK=T)
odbcCloseAll()
It also works great, but how can I append lines? This function allows me 
to append new sheets in the file, but I would also like to append new 
lines of data onto one of the sheets. How can I do that?

- The last problem:
I would like to export a dataframe, but I get this error message:
 > save2excel(truc, "test")
Error in sqlSave(xlsFile, x, tablename = t.name, rownames = FALSE, addPK 
= T) :
   HYS21 -1508 [Microsoft][Pilote ODBC Excel] Le champ 'Group' existe 
déjà dans la table 'test'.
[RODBC] ERROR: Could not SQLExecDirect 'CREATE TABLE [test]  ("Group" 
NUMBER, "Group" NUMBER, "test" NUMBER, "crit" NUMBER, "se" NUMBER, "df" 
NUMBER)'

Here is the object:
 > dput(truc)
structure(list(Group = c(1, 1, 1, 1, 1, 2, 2, 2, 2, 3, 3, 3, 4, 4, 5), 
Group = c(2, 3, 4, 5, 6, 3, 4, 5, 6, 4, 5, 6, 5, 6, 6), test = 
c(0.907901716802262, 0.344080298502179, 0.780331168285069, 
2.15033450900747, 0.194069709110157, 0.406313481811673, 
0.116434832984871, 1.52727249397868, 0.579195268552845, 
0.420998518182892, 1.62939679051865, 0.138892090710994, 
1.11253003450962, 0.555496810201502, 1.78610263147685), crit = 
c(2.97744276941854, 2.98843563665370, 3.05786246930315, 
3.00681172135752, 2.99644239171413, 3.00036808377006, 3.07797861408659, 
3.02408697737205, 3.01060847439059, 3.03639474502811, 2.99664917266571, 
2.99135011459308, 3.04177033698215, 3.04239401519992, 3.00305006434149), 
se = c(12.1028423223510, 15.1532795810610, 16.3991441261986, 
15.3598663144688, 14.9271014453042, 14.2113088036481, 15.5329116369945, 
14.4313862483545, 13.9698880958026, 18.0115083683957, 17.0706765780184, 
16.6823518483263, 18.1856549192307, 17.8216415967046, 16.8702244895529), 
df = c(99.682919819226, 89.3039016709219, 50.9067902231679, 
76.0647290534967, 83.0087667496558, 80.2356900159524, 43.4849997568059, 
66.760479193059, 73.8040951542063, 61.4088750589742, 82.8579246229594, 
86.904905246028, 58.9562752558462, 58.5971747302359, 78.4453136851244)), 
.Names = c("Group", "Group", "test", "crit", "se", "df"), row.names = 
c(NA, -15L), class = "data.frame")

Any ideas?

Thanks a lot for your help
Ivan