title: Make a subset of dtaframe according to column value python
body: <p>I have generated dataframe frame and created a csv file now I want to make a subset of dataframe in which it checks the value of column <code>"dst"</code> (uptill 0) and then take value of <code>Image</code> column.
  My current dataframe is:</p>
  
  <pre><code>     Image   Maxval   locx  locy  dst
  0    1.jpg    0.99      22    47    0
  1    7.jpg    0.46      27    65    18.68
  2    11.jpg   0.32      18    29    18.43
  8    18.jpg   0.25      7     38    17.49
  10   1.jpg    0.99      40    71    0
  11   18.jpg   0.56      27    71    17.68
  13   7.jpg    0.42      93    17    19.43
  19   11.jpg   0.35      70    39    17.49
  </code></pre>
  
  <p>The image are sorted according to maxval so i don't want to change the order of images.I want my dataframe to be:</p>
  
  <pre><code>   Image    Image
    1.jpg     1.jpg
    7.jpg     18.jpg
    11.jpg    7.jpg
    18.jpg    11.jpg 
  </code></pre>