[R] Help with arrays

[Marc Schwartz]

On May 29, 2014, at 11:22 AM, Marc Schwartz <marc_schwartz at me.com> wrote:

> 
> 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.


Correction in the above sentence, it should be:

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

Marc