How to check if an R matrix column contains only duplicate values?

To check if an R matrix column contains only duplicate values, we can use dim function for the dimension of the column after accessing the matrix column with table function. For example, if we have a matrix called M having five columns then we can check whether first column contains only duplicate values using the command dim(table(M[,1]))==1

Example

Consider the below data frame −

 Live Demo

M1<-matrix(c(rep(1,20),rep(2,20)),ncol=2) M1

Output

    [,1] [,2] [1,]  1   2 [2,]  1   2 [3,]  1   2 [4,]  1   2 [5,]  1   2 [6,]  1   2 [7,]  1   2 [8,]  1   2 [9,]  1   2 [10,] 1   2 [11,] 1   2 [12,] 1   2 [13,] 1   2 [14,] 1   2 [15,] 1   2 [16,] 1   2 [17,] 1   2 [18,] 1   2 [19,] 1   2 [20,] 1   2

Checking whether columns in M1 contains duplicate values or not −

Example

dim(table(M1[,1]))==1

Output

[1] TRUE

Example

dim(table(M1[,2]))==1 

Output

[1] TRUE

Example

 Live Demo

M2<-matrix(c(rep(1,20),rpois(20,2)),ncol=2) M2

Output

  [,1] [,2] [1,]  1   4 [2,]  1   2 [3,]  1   2 [4,]  1   0 [5,]  1   4 [6,]  1   0 [7,]  1   3 [8,]  1   3 [9,]  1   4 [10,] 1   2 [11,] 1   0 [12,] 1   2 [13,] 1   3 [14,] 1   1 [15,] 1   2 [16,] 1   4 [17,] 1   0 [18,] 1   6 [19,] 1   5 [20,] 1   1

Checking whether columns in M2 contains duplicate values or not −

Example

dim(table(M2[,1]))==1

Output

[1] TRUE

Example

dim(table(M2[,2]))==1 

Output

[1] FALSE

Example

 Live Demo

M3<-matrix(c(rep(5,20),rnorm(20,2,0.5)),ncol=2) M3

Output

     [,1] [,2] [1,]  5  1.3875392 [2,]  5  1.0927555 [3,]  5  2.2385030 [4,]  5  2.0015805 [5,]  5  2.0743614 [6,]  5  0.5072223 [7,]  5  2.1752948 [8,]  5  1.8959838 [9,]  5  2.0886671 [10,] 5  2.5035340 [11,] 5  1.5832031 [12,] 5  1.7593074 [13,] 5  1.7983010 [14,] 5  2.6664104 [15,] 5  1.2117921 [16,] 5  2.5033426 [17,] 5  1.8175419 [18,] 5  1.7202983 [19,] 5  2.1421497 [20,] 5  1.2270815

Checking whether columns in M3 contains duplicate values or not −

Example

dim(table(M3[,1]))==1

Output

[1] TRUE

Example

dim(table(M3[,2]))==1 

Output

[1] FALSE