# [R] summation coding

Rainer Schuermann rainer.schuermann at gmx.net
Fri Oct 19 09:35:24 CEST 2012

```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.
>
>
>
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