How to find the row median of columns having same name in R matrix?

To find the row median of columns having same name in R matrix, we can follow the below steps −

• First of all, create a matrix with some columns having same name.

• Then, use tapply along with colnames and median function to find the row median of columns having same name.

Example

Create the matrix

Let’s create a matrix as shown below −

M<-matrix(rpois(150,10),ncol=6) colnames(M)<-c("C1","C1","C2","C2","C1","C2") M

Output

On executing, the above script generates the below output(this output will vary on your system due to randomization) −

      C1 C1 C2 C2 C1 C2 [1,]   7  2  7 13  4 10 [2,]  20  8 10  8 15 12 [3,]   8 11  6 19  9 11 [4,]  10 10  9  8  8 8 [5,]   7 17 10  9 9 10 [6,]   9 10  8  6 11 13 [7,]   8  7 10 11 7 13 [8,]   8 11 10 16 4 9 [9,]  12  8 13  7 8 9 [10,]  6  7  7 14 15 11 [11,]  9  6 17 12 12 13 [12,] 11  8  8 10 13 8 [13,]  9  9  9  8 6 10 [14,]  7 11 11  8 11 11 [15,] 13 13  9 10 10 12 [16,]  5 10  4 13 15 6 [17,]  8 10  6  8 12 3 [18,]  8  9 10  8 7 7 [19,] 14 14 14  8 3 11 [20,]  7 13 10  8 8 9 [21,]  7 10  8  5 15 9 [22,]  8  8  5  8 11 13 [23,]  9 13  4  9 6 19 [24,] 12 11  5  7 7 7 [25,] 14 12  8 10 12 4

Find the row median of columns having same name

Using tapply along with colnames and median function to find the row median of columns having same name in matrix M −

M<-matrix(rpois(150,10),ncol=6) colnames(M)<-c("C1","C1","C2","C2","C1","C2") t(apply(M,1, function(x) tapply(x,colnames(M),median)))

Output

      C1 C2 [1,]   4 10 [2,]  15 10 [3,]   9 11 [4,]  10  8 [5,]   9 10 [6,]  10  8 [7,]   7 11 [8,]   8 10 [9,]   8  9 [10,]  7 11 [11,]  9 13 [12,] 11  8 [13,]  9  9 [14,] 11 11 [15,] 13 10 [16,] 10 6 [17,] 10 6 [18,]  8  8 [19,] 14 11 [20,]  8 9 [21,] 10 8 [22,]  8 8 [23,]  9 9 [24,] 11 7 [25,] 12 8