check whether matrix rows equal a vector in R , vectorized

Question

I'm very surprised this question has not been asked, maybe the answer will clear up why. I want to compare rows of a matrix to a vector and return whether the row == the vector everywhere. See the example below. I want a vectorized solution, no apply functions because the matrix is too large for slow looping. Suppose there are many rows as well, so I would like to avoid repping the vector.

set.seed(1)

M = matrix(rpois(50,5),5,10)

v = c(3 ,   2 ,   7  ,  7 ,   4   , 4   , 7  ,  4  ,  5, 6)

M
     [,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10]
[1,]    4    8    3    5    9    4    5    6    7     7
[2,]    4    9    3    6    3    1    5    7    6     1
[3,]    5    6    6   11    6    4    5    2    7     5
[4,]    8    6    4    4    3    8    3    6    5     6
[5,]    3    2    7    7    4    4    7    4    5     6

Output should be

FALSE  FALSE FALSE FALSE TRUE

Answer 1

One possibility is

rowSums(M == v[col(M)]) == ncol(M)
## [1] FALSE FALSE FALSE FALSE  TRUE

Or simlarly

rowSums(M == rep(v, each = nrow(M))) == ncol(M)
## [1] FALSE FALSE FALSE FALSE  TRUE

Or

colSums(t(M) == v) == ncol(M)
## [1] FALSE FALSE FALSE FALSE  TRUE

v[col(M)] is just a shorter version of rep(v, each = nrow(M)) which creates a vector the same size as M (matrix is just a vector, try c(M) ) and then compares each element against its corresponding one using == . Fortunately == is a generic function which has an array method (see methods("Ops") and is.array(M) ) which allows us to run rowSums (or colSums ) on it in order to makes sure we have the amount of matches as ncol(M)

Answer 2

使用DeMorgan的规则（Not all = Some not），然后All equal = Not Some Not equal，我们也有

!colSums(t(M) != v)

Answer 3

The package prodlim has a function called row.match , which is easy to use and ideal for your problem. First install and load the library: library(prodlim) . In our example, row.match will return '5' because the 5th row in M is equal to v . We can then convert this into a logical vector.

m <- row.match(v, M)
m==1:NROW(M)#[1] FALSE FALSE FALSE FALSE  TRUE