Find the most repeated row in a matrix

Question

I have about 10000 replicates of a sample in a matrix. My matrix has 1000 rows and 6 columns. Numbers in the columns range from 0:58 depending on the sample.

actual.prob <- c(.14, .14, .16, .13, .19, .24)
million.rep <- replicate(10000, sample(1:6, 58, replace= T, actual.prob))
new.matrix <- matrix(nrow= 10000, ncol=6)
for(i in 1:10000){
  new.matrix[i,] <- as.vector(table(factor(million.rep[,i], levels=1:6)))
}
new.matrix[1:10,]

          [,1] [,2] [,3] [,4] [,5] [,6]
     [1,]    3    7   11   11   11   15
     [2,]    7    6   12    5   19    9
     [3,]   12    7    6    8   11   14
     [4,]    6    7   16    6   11   12
     [5,]    5    9   12    5   14   13
     [6,]    9    4   14    7   10   14
     [7,]    6    9    9    6   15   13
     [8,]    9    4    8    8   11   18
     [9,]    6   11    7    5   12   17
     [10,]    7    6    9    9   15   12

I want to find if any samples are repeated. I tried replicated() which tells me what rows are replicates, but I want to view the row without having to go back manually. Any suggestions?

Answer 1

Here is a data.table implementation:

library(data.table)
dt <- data.table(new.matrix)
head(dt[, list(repeats=.N, id=.I[[1]]), by=names(dt)][order(repeats, decreasing=T)], 20)
#     V1 V2 V3 V4 V5 V6 repeats   id
#  1:  5  7 11  8 13 14       4  543
#  2:  5 11 13  5 10 14       4  579
#  3:  6  8  6 10 12 16       4 1433
#  4:  6  9  9  9  9 16       4 1688
#  5:  8  8  9  7 10 16       4 2382
#  6:  6 10  8  7 11 16       4 2965
#  7:  7  9 11  8 11 12       4 3114
#  8:  8  8 10  7 10 15       4 3546
#  9:  7  8 12  9  9 13       4 5759
# 10:  7  7 13  9 10 12       4 9021
# 11:  8 10  8  8 12 12       3   81
# 12:  9 10  7  7 11 14       3  110
# 13:  7 11  8  6 12 14       3  130
# 14: 11  9  7  7  9 15       3  143
# 15:  8 10 10  7 11 12       3  330
# 16:  8  9 10  8 13 10       3  480
# 17:  9 10  7 10 11 11       3  542
# 18:  8  6 11  9 11 13       3  555
# 19:  7 10  7  6 10 18       3  577
# 20:  7  8 10  5 12 16       3  601   

where repeats is how many times a row shows up, and id the first row in the matrix that matches that pattern.