CODEWITHSUNDEEP
rmatrix
Comp_Warrior
Comp_Warrior

Reputation: 179

Retrieve row number if row is identical to specified vector

Consider the following matrix:

MAT <- matrix(nrow=3,ncol=3,1:9)
     [,1] [,2] [,3]
[1,]    1    4    7
[2,]    2    5    8
[3,]    3    6    9

I want to retrieve the row number if I provide a vector which exactly matches a row in MAT. So if I provide c(2,5,8), I should get back 2. I'm unsure how to accomplish this; the closest thing I know is using which to find the location of a single number in a matrix. An alternate could be a very slow quadruple for loop checking if the given vector matches a row in the matrix. Is there a one line solution for this problem?

Upvotes: 0

Views: 687

Answers (2)

James
James

Reputation: 66844

You can use identical to test, apply loop and which to identify:

which(apply(MAT,1,function(x) identical(x,c(2L,5L,8L))))
[1] 2

Note that the values in the matrix are stored as integers, so you need to specify that in the vector to test.

Upvotes: 3

Marius
Marius

Reputation: 60070

You can apply a simple matching function to each row, then use which to find the row number:

search_vec = c(2, 5, 8)

vec_matches = apply(MAT, 1, function(row, search_vec) all(row == search_vec), search_vec)
row_num = which(vec_matches)

Upvotes: 2

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