How to find the coordinate of a value in an R matrix?

The coordinate of a value in an R matrix is the row and column intersection that is the row and column index for that particular value. This can be found by using which function.

For example, if we have a matrix called M that contains value starting from 1 to 20 then we can find the coordinate of value 5 by using the command given below −

which(M==5,arr.ind=TRUE)

Example

Following snippet creates a matrix −

M1<-matrix(rpois(80,10),ncol=4)
M1

The following matrix is created −

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

To find the coordinates of value 11 in M1, add the following code to the above snippet −

M1<-matrix(rpois(80,10),ncol=4)
which(M1==11,arr.ind=TRUE)

Output

If you execute all the above given snippets as a single program, it generates the following output −

     row col
[1,]   4  2
[2,]   6  2
[3,]   7  2
[4,]  18  2
[5,]  12  3
[6,]  14  3
[7,]  15  3
[8,]  19  3
[9,]   1  4
[10,]  7  4
[11,] 10  4

Example 2

Following snippet creates a matrix −

M2<-matrix(rpois(80,2),ncol=4)
M2

The following matrix is created −

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

To find the coordinates of value 4 in M2, add the following code to the above snippet −

M2<-matrix(rpois(80,2),ncol=4)
which(M2==4,arr.ind=TRUE)

Output

If you execute all the above given snippets as a single program, it generates the following output −

     row col
[1,]  9  1
[2,] 10  1
[3,] 13  1
[4,] 20  1
[5,] 13  2
[6,] 13  3
[7,] 14  3
[8,] 18  3

Example 3

Following snippet creates a matrix −

M3<-matrix(rpois(40,5),ncol=2)
M3

The following matrix is created −

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

To find the coordinates of value 8 in M3, add the following code to the above snippet −

M3<-matrix(rpois(40,5),ncol=2)
which(M3==8,arr.ind=TRUE)

Output

If you execute all the above given snippets as a single program, it generates the following output −

    row col
[1,] 10  1
[2,] 11  1
[3,] 15  2
[4,] 20  2