Assuming that you actually mean
a1(b2+b3+b4) + a2(b1+b3+b4) + a3(b1+b2+b4) + a4(b1+b2+b3)
^ ^ ^
this might give you what you want:
x <- data.frame( a = sample( 1:10, 4 ), b = sample( 11:20, 4 ) )
x
a b
1 1 16
2 7 15
3 8 19
4 4 13
for( i in 1 : length( x$a ) )
x$c[i] <- x$a[i] * ( sum( x$b ) - x$b[i] )
x
a b c
1 1 16 47
2 7 15 336
3 8 19 352
4 4 13 200
Rgds,
Rainer
On Thursday 18 October 2012 12:33:39 djbanana wrote:
> I would like to code the following in R: a1(b1+b2+b3) + a2(b1+b3+b4) +
> a3(b1+b2+b4) + a4(b1+b2+b3)
>
> or in summation notation: sum_{i=1, j\neq i}^{4} a_i * b_i
>
> I realise this is the same as: sum_{i=1, j=1}^{4} a_i * b_i - sum_{i=j} a_i
> * b_i
>
> would appreciate some help.
>
> Thank you.
>
>
>
> --
> View this message in context:
> http://r.789695.n4.nabble.com/summation-coding-tp4646678.html
> Sent from the R help mailing list archive at Nabble.com.
>
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