title: TypeError: 'int' object is not iterable when iterating through pandas column
body: <p>I have a simple use case. I want to read a text file into a pandas file and iterate through the unique <strong><em>id</em></strong> s to plot a <strong><em>x-y graph</em></strong>.
  Worked for me fine at many other projects but now i get the <code>TypeError: 'int' object is not iterable</code>. 
  At first I got <code>TypeError: 'numpy.float64' object is not iterable</code>that is why I changed the type of <em>id</em> to <em>int</em> (see code). But that does not work either. I do not see why. Any ideas?</p>
  
  <pre><code>f = open(file,"r+")
  with open(file,"r+") as f1:
      data10 = f1.read()
      TESTDATA = StringIO(data11)
  df = pd.read_table(TESTDATA, sep=" ")
  df.columns = ["x", "y", "id"]
  
  #Astype because i got the error TypeError: 'numpy.float64' object is not iterable
  df.id = df.id.astype(int)
  
  #get unique values of column id
  list1=df['id'].tolist()
  list1=list(set(list1))
  fig, ax = plt.subplots()
  for i ,g in list1:
      x = df[df.id==i]['x']
      y = df[df.id==i]['y']
      g.plot(x='x',y='x', marker='o', ax=ax, title="Evaluation")
  </code></pre>