Shmoose - 1 year ago 65
R Question

# randomized element-wise multiplication in R

I've been digging around the site for an answer to my question, and I'm new with R so I'm hoping this is even possible. I have two large matrices of simulations (A = 100,000 x 50 and B = 10,000 x 50) that I would like to randomly multiply element-wise by row.

Essentially I would like each row in A to randomly select a row from B for element-wise multiplication.

A:

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

And
B:

``````      [,1] [,2] [,3] [,4] [,5]
[1,]    1    1    1    1    1
[2,]    2    2    2    2    2
[3,]    3    3    3    3    3
[4,]    4    4    4    4    4
[5,]    5    5    5    5    5
``````

Is there an operator that could go through A's rows and randomly select a row from B to pair for element wise multiplication? For results something like this:

`````` C <- A&*&B
C
A[1,]*B[3,]
A[2,]*B[1,]
A[3,]*B[2,]
A[4,]*B[5,]
A[5,]*B[3,]
A[6,]*B[4,]
A[7,]*B[1,]
A[8,]*B[5,]
A[9,]*B[2,]
A[10,]*B[2,]
``````

Thanks!

Try this:

``````row_id <- sample(1:nrow(B), nrow(A), replace = TRUE)
A * B[row_id, ]
``````

I think I only need to explain what `sample()` does. Consider:

``````sample(1:5, 10, replace = TRUE)
[1] 4 5 2 4 1 2 2 1 2 5
``````

I did not set random seed by `set.seed()`, so when you run it, you will get different result. But all you need to know is that: it is random.

Recommended from our users: Dynamic Network Monitoring from WhatsUp Gold from IPSwitch. Free Download