[R] problem in do.call function

[Duncan Murdoch]

On 08/08/2011 4:34 AM, Kathie wrote:
> Dear all,
>
> I am trying to use "do.call", but I don't think I totally understand this
> function.
>
> Here is an simple example.
>
> --------------------------------------------
>
> >  B<- matrix(c(.5,.1,.2,.3),2,2)
> >  B
>       [,1] [,2]
> [1,]  0.5  0.2
> [2,]  0.1  0.3
> >  x<- c(.1,.2)
> >  X<- cbind(1,x)
> >  X
>           x
> [1,] 1 0.1
> [2,] 1 0.2
> >
> >  lt<- expand.grid(i=seq(1,2), y0=seq(0,2))
> >  lt
>    i y0
> 1 1  0
> 2 2  0
> 3 1  1
> 4 2  1
> 5 1  2
> 6 2  2
> >
> >  fc<- function(y0,i) dpois(y0, exp(rowSums(t(X[i,])*B[,1])))
> >
> >  do.call(fc,lt)
> [1] 1.892179e-09 3.348160e-01 3.800543e-08 3.663470e-01 3.816797e-07
> 2.004237e-01
>
> --------------------------------------------
>
> Unfortunately, what I want to get is
>
> dpois(0, exp(rowSums(t(X[1,])*B[,1]))) = 0.1891356
> dpois(0, exp(rowSums(t(X[2,])*B[,1]))) = 0.1859965
> dpois(1, exp(rowSums(t(X[1,])*B[,1]))) = 0.3149658
> dpois(1, exp(rowSums(t(X[2,])*B[,1]))) = 0.3128512
> dpois(2, exp(rowSums(t(X[1,])*B[,1]))) = 0.2622549
> dpois(2, exp(rowSums(t(X[2,])*B[,1]))) = 0.2631122
>
> --------------------------------------------
>
> Would you plz tell me why these two results are different?? and how do I get
> what I want to using "do.call" function??

Your function expects arguments in the order y0, i, but you are passing 
them in the order i, y0.  Change the header of your function or the 
order of the columns in lt.

Duncan Murdoch