data.frame - how to calculate the number of rows

this works now,

cbind(summaryBy(B+C~ A,  data=df, FUN=c(mean, var)),
'numrows'=as.numeric(table(df$A)))


but now, I cannot add another column D beside A, as I do before, like

cbind(summaryBy(B+C~ A+D,  data=df,FUN=c(mean, var)),
'numrows'=as.numeric(table(df$A)))

because of this D, I got the following error message in german:
<<Fehler in data.frame(..., check.names = FALSE) :  Argumente implizieren
unterschiedliche Anzahl Zeilen: 21, 18>>

<<error in data.frame(...., check.names = FALSE): arguments has differents
counts of rows: 21, 18>>

has anybody an idea, what I can do ?




On 26/12/2007, Agrarimmobilien <ralf.pfeiffer at agrarimmobilien.info> wrote:

Hello,

I had to give some more information to my posting:

as ouput there are more than one row, depending on the values of column 
A
(transformierung to distinct values, here 3 and 4, but there are much
more)

       A            B                C
1      3             6                 5
2      3             4                 20
3      3             8                 2
4      4             8                 3
5      4             2                 6

Output:

       A            B                C                      num rows
1      3            6                 6.16                  3
2      4            5                 4.00                  3

B is mean and C variance.


thank you
Macki

Hello,

it seems to be a simple problem, but  I couldn't find an answer in the
archiv. (I think, it must has something to do with the group-select,
like
in
php)

I've the following data.frame:

       A            B                C
1      3             6                 5
2      4             4                 20
3      5             8                 2

I want to get the number of the rows in the 4th column, like:

       A            B                C                      num rows
1      3            6                 6.16                  3


(B is mean, C is variance by using summaryBy(B+C~ A,  data=daten,
FUN=c(mean,var))  from the doBy-package)

But, how can I add the column 'numrow' and count the number of the 
rows?

Thanks!

Macki

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