[R] Need help to split a given matrix is a "sequential" way

[Megh]

I need to split a given matrix in a sequential order. Let my matrix is :

> dat <- cbind(sample(c(100,200), 10, T), sample(c(50,100, 150, 180), 10,
> T), sample(seq(20, 200, by=20), 10, T)); dat
      [,1] [,2] [,3]
 [1,]  200  100   80
 [2,]  100  180   80
 [3,]  200  150  180
 [4,]  200   50  140
 [5,]  100  150   60
 [6,]  100   50   60
 [7,]  100  100  100
 [8,]  200  150  100
 [9,]  100   50  120
[10,]  200   50  180

Now I need to split above matrix according to unique numbers in the 2nd
column. Therefore I have following :

> dat1 <- dat[which(dat[,1] == unique(dat[,1])[1]),]
> dat2 <- dat[-which(dat[,1] == unique(dat[,1])[1]),]; dat1; dat2
     [,1] [,2] [,3]
[1,]  200  100   80
[2,]  200  150  180
[3,]  200   50  140
[4,]  200  150  100
[5,]  200   50  180
     [,1] [,2] [,3]
[1,]  100  180   80
[2,]  100  150   60
[3,]  100   50   60
[4,]  100  100  100
[5,]  100   50  120

Now each of dat1 and dat2 needs to be splited according to the it's 2nd
column i.e. 

> dat11 <- dat1[which(dat1[,2] == unique(dat1[,2])[1]),]
> dat12 <- dat1[which(dat1[,2] == unique(dat1[,2])[2]),]
> dat13 <- dat1[which(dat1[,2] == unique(dat1[,2])[3]),]; dat11; dat12;
> dat13
[1] 200 100  80
     [,1] [,2] [,3]
[1,]  200  150  180
[2,]  200  150  100
     [,1] [,2] [,3]
[1,]  200   50  140
[2,]  200   50  180

similarly for dat2..............

This kind of sequential spliting would continue for
(no_of_cols_of_ogirinal_matrix -1) times. It would be greate if again I can
put all those matrices within a "list" object for further calculations.

Therefore you see if the original matrix is of small_size then that can be
handled manually. However for a moderately large matrix that task would be
very clumbersome. Therefore I am looking for some mechanized way to do that
for an arbitrary matrix.

Can anyone here help me on this regard?

Thank you so much for your kind attention.

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