[R] new_index

[Val]

Hi All,

I have two data frames   with thousand  rows  and several columns. My
samples of the data frames are shown below

dat1 <-read.table(text="ID, x, y, z
ID , x, y, z
A, 10,  34, 12
B, 25,  42, 18
C, 14,  20,  8 ",sep=",",header=TRUE,stringsAsFactors=F)

dat2 <-read.table(text="ID, x, y, z
ID, weight
A,  0.25
B,  0.42
C,  0.65 ",sep=",",header=TRUE,stringsAsFactors=F)

My goal is to  create an index value  for each ID  by mutliplying the
first row of dat1 by the second  column of dat2.

  (10*0.25 ) + (34*0.42) + (12*0.65)=  24.58
  (25*0.25 ) + (42*0.42) + (18*0.65)=  35.59
  (14*0.25 ) + (20*0.42) + (  8*0.65)=  19.03

The  desired out put is
dat3
ID, Index
A 24.58
B  35.59
C  19.03

How do I do it in an efficent way?

Thank you,