Example

 
> a = rand(3,5)
 a =
    0.572      0.109      0.929      0.281      0.436  
    0.576      0.902      0.935      0.972      0.625  
    0.501      0.568      0.771     0.0269      0.469  
> mean(a)
     0.55      0.526      0.878      0.427       0.51  
> b = a[1;]
 b =
    0.572      0.109      0.929      0.281      0.436  
> mean(b)
    0.465
> c = a[;1]
 c =
    0.572  
    0.576  
    0.501  
> mean(c)
     0.55