title: why dim of colMeans/rowMeans return null?
body: <p>I am new to R. I have the following code</p>
  
  <pre><code>sigma1  = matrix(c(2,0,0,1),2,2)
  mu1     = matrix(c(0,10),2,1)
  
  x1      = t(mvrnorm(n = 5, mu1, sigma1))
  
  print(rowMeans(x1))
  print(dim(colMeans(x1)))
  </code></pre>
  
  <p>and for some reason I get NULL for dimension of row/col means.</p>