title: How can i make an empty matrix that ican fill it out later by floats and strings
body: <p>I want to make a matrix that at the first of program, i can't understand how many rows it has and during the program i will add each row to the matrix by using "vstack".</p>
  
  <p><strong>Each row of these matrix consist of 100 elements,some strings and some floats.</strong></p>
  
  <pre><code>Y=[]
  </code></pre>
  
  <p>and later during the program i will make a new row in y array and i want to add it to Y.</p>
  
  <pre><code>Y=numpy.vstack([Y,y])
  </code></pre>
  
  <p>The error:</p>
  
  <pre><code>return _nx.concatenate([atleast_2d(_m) for _m in tup], 0)
  
  
  ValueError: all the input array dimensions except for the concatenation axis must match exactly
  </code></pre>
  
  <p>I know that  for using "vstack" I need to have "Y" with the same dimension s as y but here I don't know how can i define that.</p>
  
  <p>I tried this way too:</p>
  
  <pre><code>Y=[]
  </code></pre>
  
  <p>And later by using h starting from 0 <code>Y[h]=y</code></p>
  
  <p>Error: <code>IndexError: list assignment index out of range</code></p>