CODEWITHSUNDEEP
rmatrixvector
fsbmat
fsbmat

Reputation: 301

Test if a row of a matrix equals a given vector

How to construct a function that evaluates if any line of matrix mat is equal to vector vec in code below:

set.seed(000)
mat <- matrix(rnorm(20),4,5)
vec <- c(1.3297993, -0.9285670,  0.7635935, -0.2992151,  0.4356833)
mat[3,]
vec
mat==vec

Also, how determine if at least one vec value is in mat?

Note: mat == vec should be equal to TRUE, ie mat-vec == 0 if mat-vec <tol, where tol = 1e-5.

Upvotes: 1

Views: 261

Answers (2)

jess
jess

Reputation: 534

First of all, your example won't work because of the floating point trap (starting on page 9).

This should do the trick: 

set.seed(000)
mat <- round(matrix(rnorm(20),4,5), digits = 7)
vec <- c(1.3297993, -0.9285670,  0.7635935, -0.2992151,  0.4356833)

Now, mat[3, ] == vec is true.

If you want to know if one row of mat matches vec, try: 

apply(mat, 1, function(x) identical(x, vec))

To find out if at least one value of vec is in mat, you can do: 

length(vec[which(vec %in% mat)])

The result reflects the number of matches found between your vector and your matrix.

Upvotes: 3

Hong Ooi
Hong Ooi

Reputation: 57686

Something like this:

compare <- function(mat, vec, tol=1e-5)
{
    ok <- apply(mat, 1, function(v) {
        all(abs(v - vec) < tol)
    })
    any(ok)
}


v <- 1:5
m <- matrix(rnorm(25), nrow=5)
compare(m, v)
# FALSE

m[1,] <- v
compare(m, v)
# TRUE

Upvotes: 2

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