title: Looping structure and Pandas
body: <p>I'm learning python and with it pandas and some tools about Data Science. Doing the exercises of a book I wrote the above code on IPython but I receive an error message when the block is executed:</p>
  
  <pre><code>for i in range(len(df1)):
      if (df1['Temperature'][i]-df1['Temperature'][i-1]) &gt; 0.1:
          print (df1['Temperature'][i])
  </code></pre>
  
  <p>Traceback (most recent call last):</p>
  
  <pre><code>File "&lt;ipython-input-140-9f31dd23b324&gt;", line 2, in &lt;module&gt;
      if (df1['Temperature'][i]-df1['Temperature'][i-1]) &gt; 0.1:
  
    File "D:\Programas\Anaconda\lib\site-packages\pandas\core\series.py", line 766, in __getitem__
      result = self.index.get_value(self, key)
  
    File "D:\Programas\Anaconda\lib\site-packages\pandas\core\indexes\base.py", line 3103, in get_value
      tz=getattr(series.dtype, 'tz', None))
  
    File "pandas\_libs\index.pyx", line 106, in pandas._libs.index.IndexEngine.get_value
  
    File "pandas\_libs\index.pyx", line 114, in pandas._libs.index.IndexEngine.get_value
  
    File "pandas\_libs\index.pyx", line 162, in pandas._libs.index.IndexEngine.get_loc
  
    File "pandas\_libs\hashtable_class_helper.pxi", line 958, in pandas._libs.hashtable.Int64HashTable.get_item
  
    File "pandas\_libs\hashtable_class_helper.pxi", line 964, in pandas._libs.hashtable.Int64HashTable.get_item
  
  KeyError: -1
  </code></pre>
  
  <p>Where df1['Temperature'] is a Data Frame such that Temperature is one of its columns. The code intending to compare two consecutive values of that column and verify the numeric difference between them and print the temperature given a statement. What am I doing wrong?</p>