title: Write files with multiple columns to array
body: <p>I have several files with x and y values and I want to plot them simultaniously into one graph.
  For this, I want to make a loop in which the program writes the x-data and the y-data, so that I have in the end an array which look like this:</p>
  
  <pre><code>results=[[x1],[y1],[x2],[y2],....]
  </code></pre>
  
  <p>Afterwards I want to plot all data in one graph but with different colors. And this automatically.</p>
  
  <p>Edit: my code looks at the moment like this:</p>
  
  <pre><code>#Program to show FFT intensitys of interfering waves with phase difference
  path='pah_to_files'
  files=['0pi.txt','0.25pi.txt','0.5pi.txt','0.75pi.txt','1pi.txt']
  
  #read data
  for i in range (len(files)):
      data=np.loadtxt(path+'/'+files[i], usecols=(0,1))
      position=data[:,0] #first column is position
      intensity=data[:,1] #second column is intensity
  </code></pre>
  
  <p>I know that this loop reads the files, but it always overwrites the previous position and intensity data.</p>