CODEWITHSUNDEEP
r
Timothée HENRY
Timothée HENRY

Reputation: 14614

R - How to vectorize the calculation in a 2d matrix?

I would like to create a matrix of n x n dimension, with the values

f = matrix(0,n,n)
for (x in (1:n)) {
    for (y in (1:n)) {
        f[x,y] = x^2 + y^2
    }
}

Is there a way to vectorize this (to avoid the two loops) to speed the program?

Upvotes: 0

Views: 129

Answers (2)

dickoa
dickoa

Reputation: 18437

You can use outer 

outer(x, y, function(x, y) x^2 + y^2)

For example 

x <- 1:4
y <- 2:5
outer(x, y, function(x, y) x^2 + y^2)
     [,1] [,2] [,3] [,4]
[1,]    5   10   17   26
[2,]    8   13   20   29
[3,]   13   18   25   34
[4,]   20   25   32   41

Upvotes: 6

Zbynek
Zbynek

Reputation: 5955

What about this?

n <- 10
M <- matrix(rep(1:n,n), ncol=n, byrow=T)
f <- (M**2)+t((M**2))
f

Upvotes: 1

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