Removing rows in R based on values in a single column

Question

I have anx 3 matrix in R and want to remove all rows where the last column is less than x. What is the best way to do this?

Answer 1

You could also use the subset() function.

a <- matrix(1:9, nrow=3)  
threshhold <- 8  
subset(a, a[ , 3] < threshhold)  

Answer 2

Same approach as @JeffAllen but in a little more detail and generalisable to a matrix of any size.

    data <- rbind(c(1,2,3), c(1, 7, 4), c(4,6,7), c(3, 3, 3), c(4, 8, 6))
    data
         [,1] [,2] [,3]
    [1,]    1    2    3
    [2,]    1    7    4
    [3,]    4    6    7
    [4,]    3    3    3
    [5,]    4    8    6
    #
    # set value of x
    x <- 3
    # 
    # return matrix that contains only those rows where value in 
    # the final column is greater than x. 
    # This will scale up to a matrix of any size 
    data[data[,ncol(data)]>x,]
         [,1] [,2] [,3]
    [1,]    1    7    4
    [2,]    4    6    7
    [3,]    4    8    6

Answer 3

m <- matrix(rnorm(9), ncol=3)
m <- m[m[,3]>0,]

Creates a matrix, then redefines that matrix only to include those rows in which the third column is greater than 0 ( m[,3] > 0 ).