# [R] Successively eliminating most frequent elemets

Balazs Torma torma at ilab.sztaki.hu
Wed Aug 8 15:33:58 CEST 2007

```Dear experts,

I have a 10x2 matrix T containing random integers. I would like to delete pairs (rows) iteratively, which contain the most frequent element either in the first or second column:

T <- matrix(trunc(runif(20)*10), nrow=10, ncol=2)

G <- matrix(0, nrow=6, ncol=2)

for (i  in (1:6)){
print("****************** Start iteration " ~i~ " *******************")
print("Current matrix:")
print(T)

m <- append(T[,1], T[,2])

print("Concatenated columns:")
print(m)

# build frequency table
F <- data.matrix(as.data.frame(table(m)))

dimnames(F)<-NULL

# pick up the most frequent element: sort decreasing and take is from the top
F <- F[order(F[,2], decreasing=TRUE),]

print("Freq. table:")
print(F[1:5,])

todel <- F[1,1] #rows containing the most frequent element will be deleted
G[i,1] <- todel
G[i,2] <- F[1,2]

print("todel="~todel)

# eliminate rows containing the most frequent element
# either the first or the second column contains this element
id <- which(T[,1]==todel)
print("Indexes of rows to be deleted:")
print(id)
if (length(id)>0){
T <- T[-1*id, ]
}

id <- which(T[,2]==todel)
print("Indexes of rows to be deleted:")
print(id)
if (length(id)>0){
T <- T[-1*id, ]
}

print("nrow(T)="~nrow(T))

}

print("Result matrix:")
print(G)

The output of the first two iterations looks like as follows. As one can see, the frequency table in the second iteration still contains the element deleted in the first iteration! Is this a bug or what am I doing here wrong?
Any help greatly appreciated!

 "****************** Start iteration 1 *******************"
 "Current matrix:"
[,1] [,2]
[1,]    2    2
[2,]    6    7
[3,]    9    9
[4,]    3    5
[5,]    4    0
[6,]    7    9
[7,]    5    7
[8,]    1    7
[9,]    9    6
[10,]    3    3
 "Concatenated columns:"
 2 6 9 3 4 7 5 1 9 3 2 7 9 5 0 9 7 7 6 3
 "Freq. table:"
[,1] [,2]
[1,]    8    4
[2,]    9    4
[3,]    4    3
[4,]    3    2
[5,]    6    2
 "todel=8"
 "Indexes of rows to be deleted:"
integer(0)
 "Indexes of rows to be deleted:"
integer(0)
 "nrow(T)=10"
 "****************** Start iteration 2 *******************"
 "Current matrix:"
[,1] [,2]
[1,]    2    2
[2,]    6    7
[3,]    9    9
[4,]    3    5
[5,]    4    0
[6,]    7    9
[7,]    5    7
[8,]    1    7
[9,]    9    6
[10,]    3    3
 "Concatenated columns:"
 2 6 9 3 4 7 5 1 9 3 2 7 9 5 0 9 7 7 6 3
 "Freq. table:"
[,1] [,2]
[1,]    8    4
[2,]    9    4
[3,]    4    3
[4,]    3    2
[5,]    6    2
 "todel=8"
 "Indexes of rows to be deleted:"
integer(0)
 "Indexes of rows to be deleted:"
integer(0)
 "nrow(T)=10"
 "****************** Start iteration 3 *******************"
 "Current matrix:"
...

```