title: How to concatenate vectors to create a array in loop?
body: <p>I have a loop <code>for</code> that generate a new vector <code>(100,)</code> in each iteration.  So the code loop likes</p>
  
  <pre><code>for i in range (10):
     for j in range (4):
       #Create a new vector (100,) 
       #Concatenate 4 vector together to make (400,) #400=4*10 
  #Append the concatenation vectors (400,) in vertical to make (10,400) array
  </code></pre>
  
  <p>My expected is that generates a matrix size of <code>(10,400)</code> that concatenate vectors in these loops</p>
  
  <p>Currently, my solution is</p>
  
  <pre><code>   matrix_= np.empty([10,400])
      for i in range (10):
         vector_horz=[]
         for j in range (4):
           #Create a new vector (100,) 
           vector_rnd=#Random make a vector/list with size of (100,1)
           #Concatenate 4 vector together to make (400,) #400=4*10
           vector_horz.append(vector_rnd)
      #Append the concatenation vectors (400,) in vertical to make (10,400) array
         matrix_(:,i)=vector_horz
  </code></pre>
  
  <p>However, it said that my size of <code>matrix</code> and <code>vector_horz</code> cannot assign. Could you give me another solution?</p>