R help - Sep 2010 - multiplying values in data frame by corresponding value in the first column

I am sure there is a simple solution to this... I have a column in a 
data frame specifying a grouping (1, -1) for my observations, and need 
to mutliply each observation in all the other columns of the data frame 
by the corresponding value in the given column. I played with apply, and 
saw some suggestions for sweep, but did not manage to get it working.

My table contains NAs....

Example of table as data frame
Observation Group Param1 Param2
AA                1        3        4
BB                -1        5        6


Expected result:
Observation Group Param1 Param2
AA                1        3        4
BB                -1        -5        -6

group<-as.vector(table$Group)
I extracted the first column into a vector, and am looking for a way to 
multiply each of the columns... SO far, only manual solutions (uglyyyy) 
work: table$Param1<-group*table$Param1

Thanks many times!
Martin

On Sep 21, 2010, at 3:00 PM, Martin Tomko wrote:
> I am sure there is a simple solution to this... I have a column in a data
frame specifying a grouping (1, -1) for my observations, and need to mutliply
each observation in all the other columns of the data frame by the corresponding
value in the given column. I played with apply, and saw some suggestions for
sweep, but did not manage to get it working.
> 
> My table contains NAs....
> 
> Example of table as data frame
> Observation Group Param1 Param2
> AA                1        3        4
> BB                -1        5        6
> 
> 
> Expected result:
> Observation Group Param1 Param2
> AA                1        3        4
> BB                -1        -5        -6
> 
> group<-as.vector(table$Group)
> I extracted the first column into a vector, and am looking for a way to
multiply each of the columns... SO far, only manual solutions (uglyyyy) work:
table$Param1<-group*table$Param1
> 
> Thanks many times!
> Martin

One approach is to use ?transform:
> DF
  Observation Group Param1 Param2
1          AA     1      3      4
2          BB    -1      5      6

> transform(DF, Param1 = Param1 * Group, Param2 = Param2 * Group)
  Observation Group Param1 Param2
1          AA     1      3      4
2          BB    -1     -5     -6


However, that is likely to get tedious with a large number of columns to the
right of 'Group', presuming that your actual data may be wider than the
above example. Thus, another approach may be:

DF[, -c(1:2)] <- DF[, -c(1:2)] * DF$Group
> DF
  Observation Group Param1 Param2
1          AA     1      3      4
2          BB    -1     -5     -6


HTH,

Marc Schwartz

Thank you Marc, that was an elegant solution, works perfectly!
Martin

On 9/21/2010 10:24 PM, Marc Schwartz wrote:
> DF[, -c(1:2)]<- DF[, -c(1:2)] * DF$Group
>