[R] In which column and in which row a number is in a matrix

Charles Novaes de Santana charles.santana at gmail.com
Wed Jan 2 12:36:09 CET 2013

```Ups... sorry, guys! Basic mistake: I forgot to look for the
information in the help of the function.

Thank you, Gerrit, for the information! All the best!

Charles

On Wed, Jan 2, 2013 at 12:21 PM, Gerrit Eichner
<Gerrit.Eichner at math.uni-giessen.de> wrote:
> Hi, Charles,
>
> see
>
> ?which
>
> and learn about the argument arr.ind.
>
>  Happy new year  --  Gerrit
>
>
>
> On Wed, 2 Jan 2013, Charles Novaes de Santana wrote:
>
>> Dear all, Happy New Year for all of you! I hope we have an year of
>> essential freedom for everyone!
>>
>> I am trying to manipulate a matrix in order to know in which column
>> and in which row a number is allocated. But, when we use the function
>> "which" it returns the position of the number in the "vector
>> representation of the matrix". For example:
>>
>>> mata<-matrix(2:7,nrow=2,ncol=3)
>>> mata
>>
>>     [,1] [,2] [,3]
>> [1,]    2    4    6
>> [2,]    3    5    7
>>>
>>> matb<-matrix(2:7,nrow=3,ncol=2)
>>> matb
>>
>>     [,1] [,2]
>> [1,]    2    5
>> [2,]    3    6
>> [3,]    4    7
>>>
>>> which(mata==4)
>>
>> [1] 3
>>>
>>> which(matb==4)
>>
>> [1] 3
>>
>> The function "which" returns the position "3" for both, mata and matb,
>> but If I didn't know that mata is a 2x3 matrix and matb is a 3x2, I
>> wouldn't know that the number 4 is at the column 2 and row 1 of the
>> mata and at the column 1 and row 3 of the matb. Do you know any way to
>> know the column and the row of a number in a matrix automatically?
>>
>> Thanks, best regards,
>>
>> Charles
>>
>>
>> --
>> Um axé! :)
>>
>> --
>> Charles Novaes de Santana
>> http://www.imedea.uib-csic.es/~charles
>> PhD student - Global Change
>> Laboratorio Internacional de Cambio Global
>> Department of Global Change Research
>> Instituto Mediterráneo de Estudios Avanzados(CSIC/UIB)
>> Calle Miquel Marques 21, 07190
>> Esporles - Islas Baleares - España
>>
>> Office phone - +34 971 610 896
>> Cell phone - +34 660 207 940
>>
>> ______________________________________________
>> R-help at r-project.org mailing list
>> https://stat.ethz.ch/mailman/listinfo/r-help
>> http://www.R-project.org/posting-guide.html
>> and provide commented, minimal, self-contained, reproducible code.

--
Um axé! :)

--
Charles Novaes de Santana
http://www.imedea.uib-csic.es/~charles
PhD student - Global Change
Laboratorio Internacional de Cambio Global
Department of Global Change Research