sort the rows of a dataframe and get the column values in pandas dataframe : My dataframe looks like this:
   

    COLUMN NAMES
        |5 |1  |2 |4 |3 |0 |pred_val|true_value|rank|
        ___________________________________________
      0 |0.3|0.2|0.1|0.5|0.25|0.4| 4 | 2 | 6
      1 |0.36|0.24|0.12|0.5|0.45|0.4| 4 | 3 |2  

I want to predict the values of rank column based on my true value. Like above true value is 2 for 0th row then I want to predict the rank of this row as 6 since according to all true values from 0-5, which are column names here, in their corresponding row  values true_value 2 in column has 0.1 which is the lowest in all, hence at rank 6. Likewise, for 2nd row, true_value is 3 and according to all column values, it's value is 2nd highest , so 2nd rank. 

How can I do this ? Pls help.  
      