How to subset a matrix based on values in a particular column in R?

To subset a matrix based on values in a particular column, we can use single square brackets and provide the row and column values. The column values will be set for the columns that we want to subset and the row value will be set for the values of the column using which we want to subset the matrix.

Check out the below example to understand how it works.

Example

Following snippet creates a matrix −

M<-matrix(rpois(80,5),ncol=4)
M

The following matrix is created −

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

To subset a matrix based on values in a particular column, add the following code to the above snippet −

M[,4]<-rep(c(1,2,3,4),times=5)
M

If you execute the above given snippet, it generates the following output −

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

To subset a matrix based on values in a particular column, add the following code to the above snippet −

M[M[,4]==1,c(1:3)]

If you execute the above given snippet, it generates the following output −

    [,1][,2][,3]
[1,]  8  4   6
[2,]  6  4   3
[3,]  9  6   9
[4,]  4  3   1
[5,]  5  6   3

To subset a matrix based on values in a particular column, add the following code to the above snippet −

M[M[,4]==2,c(1:3)]

If you execute the above given snippet, it generates the following output −

    [,1][,2][,3]
[1,]  5  6   1
[2,]  3  4   3
[3,]  5  4   5
[4,]  1  4   4
[5,]  8  8   3

To subset a matrix based on values in a particular column, add the following code to the above snippet −

M[M[,4]==3,c(1:3)]

If you execute the above given snippet, it generates the following output −

    [,1][,2][,3]
[1,]  5  4   7
[2,]  7  6   5
[3,]  5  8   4
[4,]  4  7   5
[5,]  8  5   4

To subset a matrix based on values in a particular column, add the following code to the above snippet −

M[M[,4]==4,c(1:3)]

If you execute the above given snippet, it generates the following output −

    [,1][,2][,3]
[1,]  3  9   1
[2,]  7  5   7
[3,]  3  2   7
[4,]  5  2   6
[5,]  2  5   6