[R] How to search an element in matrix ?

[Adaikalavan Ramasamy]

Actually, you will need to use arr.ind=TRUE which is not the default
option. You will get the results in form [i, j] indicating the i^{th}
row and j^{th} column of the element that passes the criteria.

 m <- matrix( rnorm(6), nc=3 )
 m
           [,1]     [,2]       [,3]
[1,]  0.5066194 0.786876 -1.2848658
[2,] -0.2018563 2.007892  0.4581891

which( m > 0.5, arr.ind=T )
     row col
[1,]   1   1
[2,]   1   2
[3,]   2   2

Regards, Adai


On Sun, 2005-04-10 at 21:51 -0700, Vadim Ogranovich wrote:
> A matrix is a vector as well (it is stored by columns), so it has two
> ways of indexing [i,j] and [i]. It may be easier for you to use the
> latter, thus
> which(x == 1) returns all indexes where the matrix x is equal to 1.
> 
> > -----Original Message-----
> > From: r-help-bounces at stat.math.ethz.ch 
> > [mailto:r-help-bounces at stat.math.ethz.ch] On Behalf Of tong wang
> > Sent: Sunday, April 10, 2005 9:37 PM
> > To: r-help at stat.math.ethz.ch
> > Subject: [R] How to search an element in matrix ?
> > 
> > Hi you guys,
> >      I know this might be too simple a question to post, but 
> > i searched a lot still couldn't find it.
> >     Just want to find an element in matrix and return its 
> > index , i think there should be some matrix version of 
> > "match" which only works for vector to me.
> >      thanks in advance for your help.
> > 
> > best,
> > tong
> > 
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