title: How to convert array to matrix in Julia
body: <p>I want to pick col of A(5*7) whose index is in C and calculate its inverse. However the B here is 5*1 array rather than a square matrix. How can I achieve it?</p>
  
  <pre><code>A = [1 2 1 0 0 0 0;
      1/3 1 0 1 0 0 0;
       4  1 0 0 1 0 0;
       -4 2 0 0 0 1 0;
       -6 2 0 0 0 0 1]
  C = [3 4 5 6 7]'
  
  B = [A[:,i] for i in C]
  x = inv(B)*b
  </code></pre>