A mess -- due to your continued use of html formatting.
But something like this may do what you want (hard to tell with the mess):
> m <- matrix(1:16,nrow=8)[rep(1:8,2),]
> m
[,1] [,2]
[1,] 1 9
[2,] 2 10
[3,] 3 11
[4,] 4 12
[5,] 5 13
[6,] 6 14
[7,] 7 15
[8,] 8 16
[9,] 1 9
[10,] 2 10
[11,] 3 11
[12,] 4 12
[13,] 5 13
[14,] 6 14
[15,] 7 15
[16,] 8 16
> vec <- apply(m,1,paste,collapse="-") ## converts rows into character
vector
> vec
[1] "1-9" "2-10" "3-11" "4-12" "5-13" "6-14" "7-15" "8-16" "1-9" "2-10"
"3-11" "4-12" "5-13" "6-14"
[15] "7-15" "8-16"
> ## Then maybe:
> tapply(seq_along(vec),vec, I)
$`1-9`
[1] 1 9
$`2-10`
[1] 2 10
$`3-11`
[1] 3 11
$`4-12`
[1] 4 12
$`5-13`
[1] 5 13
$`6-14`
[1] 6 14
$`7-15`
[1] 7 15
$`8-16`
[1] 8 16
> ## gives the row numbers for each unique row
There may well be slicker ways to do this -- if this is actually what you
want to do.
-- Bert
On Wed, Nov 7, 2018 at 7:56 PM li li <hannah....@gmail.com> wrote:
> Hi all,
> I use the following example to illustrate my question. As you can see,
> in matrix C some rows are repeated and I would like to find the indices of
> the rows corresponding to each of the distinct rows.
> For example, for the row c(1,9), I have used the "which" function to
> identify the row indices corresponding to c(1,9). Using this approach, in
> order to cover all distinct rows, I need to use a for loop.
> I am wondering whether there is an easier way where a for loop can be
> avoided?
> Thanks very much!
> Hanna
>
>
>
> > A <- matrix(c(1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16),8,2)> B <-
> rbind(A,A,A)> C <- as.data.frame(B[sample(nrow(B)),])> C V1 V2
> 1 1 9
> 2 2 10
> 3 3 11
> 4 5 13
> 5 7 15
> 6 6 14
> 7 4 12
> 8 3 11
> 9 8 16
> 10 5 13
> 11 7 15
> 12 2 10
> 13 1 9
> 14 8 16
> 15 1 9
> 16 3 11
> 17 7 15
> 18 4 12
> 19 2 10
> 20 6 14
> 21 4 12
> 22 8 16
> 23 5 13
> 24 6 14> T <- unique(C)> T V1 V2
> 1 1 9
> 2 2 10
> 3 3 11
> 4 5 13
> 5 7 15
> 6 6 14
> 7 4 12
> 9 8 16> > i <- 1 > which(C[,1]==T[i,1]&
> C[,2]==T[i,2])[1] 1 13 15
>
> [[alternative HTML version deleted]]
>
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[[alternative HTML version deleted]]
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