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

Gerrit Eichner Gerrit.Eichner at math.uni-giessen.de
Wed Jan 2 12:21:28 CET 2013

```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
>
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