[R] Replace value in a matrix according to a list with a list of value .

[Duncan Murdoch]

On 09/01/2014 9:25 AM, Mohammad Tanvir Ahamed wrote:
> Hi there !!
>
> I have a matrix like
> > mm
>        [,1] [,2] [,3]
>   [1,]    1   11   21
>   [2,]    2   12   22
>   [3,]    3   13   23
>
> I have a list of position index like
> > pos
>
> $row1
> [1] 1 3
>
> $row2
> [1] 3 2
>
> $row3
> [1] 1 3 2
>
> I have a list of values like
> > gty
>
> $v1
>
>   9  3
>
>
> $v2
>
>   4  8
>
>
> $v3
>
>   7  4  1
>
>   
> Now i want to replace the value of each row in mm by pos list with value gty
>
> > mm
>        [,1] [,2] [,3]
>   [1,]    9   11   3
>   [2,]    8   12   4
>   [3,]    7   1   4
>
>
> Any suggestion regarding this problem will be very helpful .
> Thank you.

Use matrix indexing.  You construct a two column matrix giving the 
indices, and then use it as an index to assign a vector of values. In 
your case, the matrix should be
1 1
1 3
2 3
2 2
3 1
3 3
3 2
(which you can create as indices <- matrix(c(1,1,1,3, ... ), ncol=2, 
byrow = TRUE)

and the vector should be 9 3 4 8 ... .  Then

mm[indices] <- vals

will do it.

Duncan Murdoch