pandas rollup question

pandas rollup

{
 "metadata": {
  "name": "pandas rollup"
 },
 "nbformat": 3,
 "nbformat_minor": 0,
 "worksheets": [
  {
   "cells": [
    {
     "cell_type": "code",
     "collapsed": false,
     "input": "import pandas as pd\nfrom pandas.tslib import Timestamp\nfrom pandas import DataFrame\n",
     "language": "python",
     "metadata": {},
     "outputs": [],
     "prompt_number": 8
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": "data = [\n{u'bug_id': 1, u'bug_when': Timestamp('1998-11-01 21:56:09'), u'removed': '', u'added': 'NEW'},\n{u'bug_id': 2, u'bug_when': Timestamp('1998-11-02 14:20:17'), u'removed': '', u'added': 'NEW'},\n{u'bug_id': 1, u'bug_when': Timestamp('1998-11-03 22:02:25'), u'removed': u'NEW', u'added': u'CLOSED'},\n{u'bug_id': 3, u'bug_when': Timestamp('1998-11-04 10:02:01'), u'removed': u'', u'added': u'NEW'},\n{u'bug_id': 2, u'bug_when': Timestamp('1998-11-04 10:02:02'), u'removed': u'NEW', u'added': u'CLOSED'},\n{u'bug_id': 3, u'bug_when': Timestamp('1998-11-05 15:03:21'), u'removed': u'NEW', u'added': u'CLOSED'}\n]",
     "language": "python",
     "metadata": {},
     "outputs": [],
     "prompt_number": 23
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": "df = DataFrame(data=data, columns=['bug_id','bug_when','removed','added'])",
     "language": "python",
     "metadata": {},
     "outputs": [],
     "prompt_number": 24
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": "df.head(n=6)",
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "html": "<div style=\"max-height:1000px;max-width:1500px;overflow:auto;\">\n<table border=\"1\" class=\"dataframe\">\n  <thead>\n    <tr style=\"text-align: right;\">\n      <th></th>\n      <th>bug_id</th>\n      <th>bug_when</th>\n      <th>removed</th>\n      <th>added</th>\n    </tr>\n  </thead>\n  <tbody>\n    <tr>\n      <td><strong>0</strong></td>\n      <td> 1</td>\n      <td> 1998-11-01 21:56:09</td>\n      <td>    </td>\n      <td>    NEW</td>\n    </tr>\n    <tr>\n      <td><strong>1</strong></td>\n      <td> 2</td>\n      <td> 1998-11-02 14:20:17</td>\n      <td>    </td>\n      <td>    NEW</td>\n    </tr>\n    <tr>\n      <td><strong>2</strong></td>\n      <td> 1</td>\n      <td> 1998-11-03 22:02:25</td>\n      <td> NEW</td>\n      <td> CLOSED</td>\n    </tr>\n    <tr>\n      <td><strong>3</strong></td>\n      <td> 3</td>\n      <td> 1998-11-04 10:02:01</td>\n      <td>    </td>\n      <td>    NEW</td>\n    </tr>\n    <tr>\n      <td><strong>4</strong></td>\n      <td> 2</td>\n      <td> 1998-11-04 10:02:02</td>\n      <td> NEW</td>\n      <td> CLOSED</td>\n    </tr>\n    <tr>\n      <td><strong>5</strong></td>\n      <td> 3</td>\n      <td> 1998-11-05 15:03:21</td>\n      <td> NEW</td>\n      <td> CLOSED</td>\n    </tr>\n  </tbody>\n</table>\n</div>",
       "output_type": "pyout",
       "prompt_number": 26,
       "text": "   bug_id             bug_when removed   added\n0       1  1998-11-01 21:56:09             NEW\n1       2  1998-11-02 14:20:17             NEW\n2       1  1998-11-03 22:02:25     NEW  CLOSED\n3       3  1998-11-04 10:02:01             NEW\n4       2  1998-11-04 10:02:02     NEW  CLOSED\n5       3  1998-11-05 15:03:21     NEW  CLOSED"
      }
     ],
     "prompt_number": 26
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": "",
     "language": "python",
     "metadata": {},
     "outputs": []
    }
   ],
   "metadata": {}
  }
 ]
}