R help - Mar 2012 - applying a function in list of indexed elements of a vector:

Hi,

I have a vector
Y1 <-c(8, 11,  7,  5,  6,  3,  6, 3,  3)
and an index
iy <-c(c(1, 2),c(1 2), c(1, 2, 3, 4), c(2, 3, 5), c(4), c(5, 6, 7), c(7, 
8, 9))

how can I produce the mean, or the sum of the elements specified in the 
index iy from the vector Y1?

expecting something like this for the sum:
Y2
19 19 31 24 5 15 12

I thought lapply function may perform this, but does not work:
Y2<-lapply(Y1[iy],sum)

Any suggestion?
TIA,

Aldi

--

Your code for iy doesn't work as provided....I'll assume you meant this
instead:

iy <- list(c(1, 2),c(1, 2), c(1, 2, 3, 4), c(2, 3, 5), c(4), c(5, 6,
7), c(7, 8, 9))

Then

sapply(iy, function(x) sum(Y1[x]))

Michael

On Sat, Mar 10, 2012 at 5:01 PM, aldi <aldi at dsgmail.wustl.edu>
wrote:
> Hi,
>
> I have a vector
> Y1 <-c(8, 11, ?7, ?5, ?6, ?3, ?6, 3, ?3)
> and an index
> iy <-c(c(1, 2),c(1 2), c(1, 2, 3, 4), c(2, 3, 5), c(4), c(5, 6, 7), c(7,
8,
> 9))
>
> how can I produce the mean, or the sum of the elements specified in the
> index iy from the vector Y1?
>
> expecting something like this for the sum:
> Y2
> 19 19 31 24 5 15 12
>
> I thought lapply function may perform this, but does not work:
> Y2<-lapply(Y1[iy],sum)
>
> Any suggestion?
> TIA,
>
> Aldi
>
> --
>
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