[R] Help with arrays

[Marc Schwartz]

On May 29, 2014, at 11:02 AM, Olivier Charansonney <olivier.charansonney at orange.fr> wrote:

> Hello,
> 
> I would like to extract the value in row 1 corresponding to the maximum in
> row 2
> 
> 
> 
> Array W
> 
>          [,1]      [,2]      [,3]      [,4]      [,5]      [,6]      [,7]
> [,8]     [,9]    [,10]
> 
> [1,] 651.00000 651.00000 651.00000 651.00000 651.00000 651.00000 651.00000
> 119.00000 78.00000 78.00000
> 
> [2,]  13.24184  13.24184  13.24184  13.24184  13.24184  13.24184  13.24184
> 16.19418 15.47089 15.47089
> 
>> valinit<-max(W[2,])
> 
>> valinit
> 
> [1] 16.19418
> 
> How to obtain ‘119’
> 
> Thanks,


Hi,

Using ?dput can help make it easier for others to recreate your object to test code:

> dput(W)
structure(c(651, 13.24184, 651, 13.24184, 651, 13.24184, 651, 
13.24184, 651, 13.24184, 651, 13.24184, 651, 13.24184, 119, 16.19418, 
78, 15.47089, 78, 15.47089), .Dim = c(2L, 10L))


W <- structure(c(651, 13.24184, 651, 13.24184, 651, 13.24184, 651, 
                 13.24184, 651, 13.24184, 651, 13.24184, 651, 13.24184, 119, 16.19418, 
                 78, 15.47089, 78, 15.47089), .Dim = c(2L, 10L))


See ?which.max, which returns the index of the *first* maximum in the vector passed to it:

> W[1, which.max(W[2, ])]
[1] 119


You should consider what happens if there is more than one of the maximum value in the first row and if it might correspond to non-unique values in the second row.

Regards,

Marc Schwartz