notes/issue_256.ipynb

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   "cells": [
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "Notes supporting [issue #256](https://github.com/alimanfoo/petl/issues/256)."
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "import petl.interactive as etl"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [],
     "prompt_number": 1
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "t1 = etl.wrap([['foo', 'bar'], [1, 'a'], [2, 'b']])\n",
      "t1"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "html": [
        "<table>\r\n",
        "<thead>\r\n",
        "<tr>\r\n",
        "<th>foo</th>\r\n",
        "<th>bar</th>\r\n",
        "</tr>\r\n",
        "</thead>\r\n",
        "<tbody>\r\n",
        "<tr>\r\n",
        "<td style='text-align: right'>1</td>\r\n",
        "<td>a</td>\r\n",
        "</tr>\r\n",
        "<tr>\r\n",
        "<td style='text-align: right'>2</td>\r\n",
        "<td>b</td>\r\n",
        "</tr>\r\n",
        "</tbody>\r\n",
        "</table>\r\n"
       ],
       "metadata": {},
       "output_type": "pyout",
       "prompt_number": 2,
       "text": [
        "+-------+-------+\n",
        "| 'foo' | 'bar' |\n",
        "+=======+=======+\n",
        "|     1 | 'a'   |\n",
        "+-------+-------+\n",
        "|     2 | 'b'   |\n",
        "+-------+-------+"
       ]
      }
     ],
     "prompt_number": 2
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "t2 = etl.wrap([['foo', 'bar'], [1, 'a'], [2, 'c']])\n",
      "t2"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "html": [
        "<table>\r\n",
        "<thead>\r\n",
        "<tr>\r\n",
        "<th>foo</th>\r\n",
        "<th>bar</th>\r\n",
        "</tr>\r\n",
        "</thead>\r\n",
        "<tbody>\r\n",
        "<tr>\r\n",
        "<td style='text-align: right'>1</td>\r\n",
        "<td>a</td>\r\n",
        "</tr>\r\n",
        "<tr>\r\n",
        "<td style='text-align: right'>2</td>\r\n",
        "<td>c</td>\r\n",
        "</tr>\r\n",
        "</tbody>\r\n",
        "</table>\r\n"
       ],
       "metadata": {},
       "output_type": "pyout",
       "prompt_number": 3,
       "text": [
        "+-------+-------+\n",
        "| 'foo' | 'bar' |\n",
        "+=======+=======+\n",
        "|     1 | 'a'   |\n",
        "+-------+-------+\n",
        "|     2 | 'c'   |\n",
        "+-------+-------+"
       ]
      }
     ],
     "prompt_number": 3
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "t3 = etl.merge(t1, t2, key='foo')\n",
      "t3"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "html": [
        "<table>\r\n",
        "<thead>\r\n",
        "<tr>\r\n",
        "<th>foo</th>\r\n",
        "<th>bar</th>\r\n",
        "</tr>\r\n",
        "</thead>\r\n",
        "<tbody>\r\n",
        "<tr>\r\n",
        "<td style='text-align: right'>1</td>\r\n",
        "<td>a</td>\r\n",
        "</tr>\r\n",
        "<tr>\r\n",
        "<td style='text-align: right'>2</td>\r\n",
        "<td>Conflict(['c', 'b'])</td>\r\n",
        "</tr>\r\n",
        "</tbody>\r\n",
        "</table>\r\n"
       ],
       "metadata": {},
       "output_type": "pyout",
       "prompt_number": 5,
       "text": [
        "+-------+----------------------+\n",
        "| 'foo' | 'bar'                |\n",
        "+=======+======================+\n",
        "|     1 | 'a'                  |\n",
        "+-------+----------------------+\n",
        "|     2 | Conflict(['c', 'b']) |\n",
        "+-------+----------------------+"
       ]
      }
     ],
     "prompt_number": 5
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "The problem with the above is that you cannot tell from inspecting *t3* alone which conflicting value comes from which source.\n",
      "\n",
      "A workaround as suggested by [@pawl](https://github.com/pawl) is to use the [*conflicts()*](http://petl.readthedocs.org/en/latest/#petl.conflicts) function, e.g.: "
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "t4 = (etl\n",
      "    .cat(\n",
      "        t1.addfield('source', 1),\n",
      "        t2.addfield('source', 2)\n",
      "    )\n",
      "    .conflicts(key='foo', exclude='source')\n",
      ")\n",
      "t4"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "html": [
        "<table>\r\n",
        "<thead>\r\n",
        "<tr>\r\n",
        "<th>foo</th>\r\n",
        "<th>bar</th>\r\n",
        "<th>source</th>\r\n",
        "</tr>\r\n",
        "</thead>\r\n",
        "<tbody>\r\n",
        "<tr>\r\n",
        "<td style='text-align: right'>2</td>\r\n",
        "<td>b</td>\r\n",
        "<td style='text-align: right'>1</td>\r\n",
        "</tr>\r\n",
        "<tr>\r\n",
        "<td style='text-align: right'>2</td>\r\n",
        "<td>c</td>\r\n",
        "<td style='text-align: right'>2</td>\r\n",
        "</tr>\r\n",
        "</tbody>\r\n",
        "</table>\r\n"
       ],
       "metadata": {},
       "output_type": "pyout",
       "prompt_number": 9,
       "text": [
        "+-------+-------+----------+\n",
        "| 'foo' | 'bar' | 'source' |\n",
        "+=======+=======+==========+\n",
        "|     2 | 'b'   |        1 |\n",
        "+-------+-------+----------+\n",
        "|     2 | 'c'   |        2 |\n",
        "+-------+-------+----------+"
       ]
      }
     ],
     "prompt_number": 9
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