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rmatrixcluster-analysis

assigning the same number to similar rows in a matrix

I have a square matrix of dimension N. I want to define a vector of size N that has as first component: all row indices of the rows of the matrix which are the same as the first row. and as second component: all row indices of the rows of the matrix which are the same as the second row.

and so on.

I am working on R and I have been trying to do that for some time now. Any idea on how to proceed would me much appreciated. 

myMatrix <- matrix(rep(1:4, 4), ncol = 2, byrow = FALSE)

     [,1] [,2]
[1,]    1    1
[2,]    2    2
[3,]    3    3
[4,]    4    4
[5,]    1    1
[6,]    2    2
[7,]    3    3
[8,]    4    4

What I have tried :

res <- list(NA)
for (i in 1:nrow(myMatrix)) {
  row_selected <- myMatrix[i,]
    res[[i]] <- which(myMatrix[i,]==row_selected)
}

res
Solution

  • The dplyr version:

    # turn the matrix into a dataframe
myDf <- myMatrix %>% as.data.frame()

myDf %>% # and now get a left join of ...
    left_join(
        myDf %>% # ...the same dataframe with the index you were looking for
            distinct_all() %>%
            mutate(index = 1:nrow(.)))