diff --git a/pandas/pandas_clean.ipynb b/pandas/pandas_clean.ipynb
index 88efc19..fec0430 100644
--- a/pandas/pandas_clean.ipynb
+++ b/pandas/pandas_clean.ipynb
@@ -1,569 +1,591 @@
 {
- "metadata": {
-  "name": "",
-  "signature": "sha256:b619f1fd1f2d4495d6a2fe9d048c09b7319b119d4e10a5b2348f0ac6f380a27c"
- },
- "nbformat": 3,
- "nbformat_minor": 0,
- "worksheets": [
+ "cells": [
   {
-   "cells": [
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "# Pandas Cleaning\n",
+    "* Replace\n",
+    "* Drop\n",
+    "* Concatenate"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 1,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [],
+   "source": [
+    "from pandas import Series, DataFrame\n",
+    "import pandas as pd"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "Setup a DataFrame:"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 2,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [
     {
-     "cell_type": "markdown",
+     "data": {
+      "text/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>population</th>\n",
+       "      <th>state</th>\n",
+       "      <th>year</th>\n",
+       "    </tr>\n",
+       "  </thead>\n",
+       "  <tbody>\n",
+       "    <tr>\n",
+       "      <th>0</th>\n",
+       "      <td> 5.0</td>\n",
+       "      <td> VA</td>\n",
+       "      <td> 2012</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>1</th>\n",
+       "      <td> 5.1</td>\n",
+       "      <td> VA</td>\n",
+       "      <td> 2013</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>2</th>\n",
+       "      <td> 5.2</td>\n",
+       "      <td> VA</td>\n",
+       "      <td> 2014</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>3</th>\n",
+       "      <td> 4.0</td>\n",
+       "      <td> MD</td>\n",
+       "      <td> 2014</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>4</th>\n",
+       "      <td> 4.1</td>\n",
+       "      <td> MD</td>\n",
+       "      <td> 2015</td>\n",
+       "    </tr>\n",
+       "  </tbody>\n",
+       "</table>\n",
+       "</div>"
+      ],
+      "text/plain": [
+       "   population state  year\n",
+       "0         5.0    VA  2012\n",
+       "1         5.1    VA  2013\n",
+       "2         5.2    VA  2014\n",
+       "3         4.0    MD  2014\n",
+       "4         4.1    MD  2015"
+      ]
+     },
+     "execution_count": 2,
      "metadata": {},
-     "source": [
-      "# Pandas Cleaning\n",
-      "* Replace\n",
-      "* Drop\n",
-      "* Concatenate"
-     ]
-    },
-    {
-     "cell_type": "code",
-     "collapsed": false,
-     "input": [
-      "from pandas import Series, DataFrame\n",
-      "import pandas as pd"
-     ],
-     "language": "python",
-     "metadata": {},
-     "outputs": [],
-     "prompt_number": 1
-    },
-    {
-     "cell_type": "markdown",
-     "metadata": {},
-     "source": [
-      "Setup a DataFrame:"
-     ]
-    },
-    {
-     "cell_type": "code",
-     "collapsed": false,
-     "input": [
-      "data_1 = {'state' : ['VA', 'VA', 'VA', 'MD', 'MD'],\n",
-      "          'year' : [2012, 2013, 2014, 2014, 2015],\n",
-      "          'population' : [5.0, 5.1, 5.2, 4.0, 4.1]}\n",
-      "df_1 = DataFrame(data_1)\n",
-      "df_1"
-     ],
-     "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>population</th>\n",
-        "      <th>state</th>\n",
-        "      <th>year</th>\n",
-        "    </tr>\n",
-        "  </thead>\n",
-        "  <tbody>\n",
-        "    <tr>\n",
-        "      <th>0</th>\n",
-        "      <td> 5.0</td>\n",
-        "      <td> VA</td>\n",
-        "      <td> 2012</td>\n",
-        "    </tr>\n",
-        "    <tr>\n",
-        "      <th>1</th>\n",
-        "      <td> 5.1</td>\n",
-        "      <td> VA</td>\n",
-        "      <td> 2013</td>\n",
-        "    </tr>\n",
-        "    <tr>\n",
-        "      <th>2</th>\n",
-        "      <td> 5.2</td>\n",
-        "      <td> VA</td>\n",
-        "      <td> 2014</td>\n",
-        "    </tr>\n",
-        "    <tr>\n",
-        "      <th>3</th>\n",
-        "      <td> 4.0</td>\n",
-        "      <td> MD</td>\n",
-        "      <td> 2014</td>\n",
-        "    </tr>\n",
-        "    <tr>\n",
-        "      <th>4</th>\n",
-        "      <td> 4.1</td>\n",
-        "      <td> MD</td>\n",
-        "      <td> 2015</td>\n",
-        "    </tr>\n",
-        "  </tbody>\n",
-        "</table>\n",
-        "</div>"
-       ],
-       "metadata": {},
-       "output_type": "pyout",
-       "prompt_number": 2,
-       "text": [
-        "   population state  year\n",
-        "0         5.0    VA  2012\n",
-        "1         5.1    VA  2013\n",
-        "2         5.2    VA  2014\n",
-        "3         4.0    MD  2014\n",
-        "4         4.1    MD  2015"
-       ]
-      }
-     ],
-     "prompt_number": 2
-    },
-    {
-     "cell_type": "markdown",
-     "metadata": {},
-     "source": [
-      "## Replace"
-     ]
-    },
-    {
-     "cell_type": "markdown",
-     "metadata": {},
-     "source": [
-      "Replace all occurrences of a string with another string, in place (no copy):"
-     ]
-    },
-    {
-     "cell_type": "code",
-     "collapsed": false,
-     "input": [
-      "df_1.replace('VA', 'VIRGINIA', inplace=True)\n",
-      "df_1"
-     ],
-     "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>population</th>\n",
-        "      <th>state</th>\n",
-        "      <th>year</th>\n",
-        "    </tr>\n",
-        "  </thead>\n",
-        "  <tbody>\n",
-        "    <tr>\n",
-        "      <th>0</th>\n",
-        "      <td> 5.0</td>\n",
-        "      <td> VIRGINIA</td>\n",
-        "      <td> 2012</td>\n",
-        "    </tr>\n",
-        "    <tr>\n",
-        "      <th>1</th>\n",
-        "      <td> 5.1</td>\n",
-        "      <td> VIRGINIA</td>\n",
-        "      <td> 2013</td>\n",
-        "    </tr>\n",
-        "    <tr>\n",
-        "      <th>2</th>\n",
-        "      <td> 5.2</td>\n",
-        "      <td> VIRGINIA</td>\n",
-        "      <td> 2014</td>\n",
-        "    </tr>\n",
-        "    <tr>\n",
-        "      <th>3</th>\n",
-        "      <td> 4.0</td>\n",
-        "      <td>       MD</td>\n",
-        "      <td> 2014</td>\n",
-        "    </tr>\n",
-        "    <tr>\n",
-        "      <th>4</th>\n",
-        "      <td> 4.1</td>\n",
-        "      <td>       MD</td>\n",
-        "      <td> 2015</td>\n",
-        "    </tr>\n",
-        "  </tbody>\n",
-        "</table>\n",
-        "</div>"
-       ],
-       "metadata": {},
-       "output_type": "pyout",
-       "prompt_number": 4,
-       "text": [
-        "   population     state  year\n",
-        "0         5.0  VIRGINIA  2012\n",
-        "1         5.1  VIRGINIA  2013\n",
-        "2         5.2  VIRGINIA  2014\n",
-        "3         4.0        MD  2014\n",
-        "4         4.1        MD  2015"
-       ]
-      }
-     ],
-     "prompt_number": 4
-    },
-    {
-     "cell_type": "markdown",
-     "metadata": {},
-     "source": [
-      "In a specified column, replace all occurrences of a string with another string, in place (no copy):"
-     ]
-    },
-    {
-     "cell_type": "code",
-     "collapsed": false,
-     "input": [
-      "df_1.replace({'state' : { 'MD' : 'MARYLAND' }}, inplace=True)\n",
-      "df_1"
-     ],
-     "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>population</th>\n",
-        "      <th>state</th>\n",
-        "      <th>year</th>\n",
-        "    </tr>\n",
-        "  </thead>\n",
-        "  <tbody>\n",
-        "    <tr>\n",
-        "      <th>0</th>\n",
-        "      <td> 5.0</td>\n",
-        "      <td> VIRGINIA</td>\n",
-        "      <td> 2012</td>\n",
-        "    </tr>\n",
-        "    <tr>\n",
-        "      <th>1</th>\n",
-        "      <td> 5.1</td>\n",
-        "      <td> VIRGINIA</td>\n",
-        "      <td> 2013</td>\n",
-        "    </tr>\n",
-        "    <tr>\n",
-        "      <th>2</th>\n",
-        "      <td> 5.2</td>\n",
-        "      <td> VIRGINIA</td>\n",
-        "      <td> 2014</td>\n",
-        "    </tr>\n",
-        "    <tr>\n",
-        "      <th>3</th>\n",
-        "      <td> 4.0</td>\n",
-        "      <td> MARYLAND</td>\n",
-        "      <td> 2014</td>\n",
-        "    </tr>\n",
-        "    <tr>\n",
-        "      <th>4</th>\n",
-        "      <td> 4.1</td>\n",
-        "      <td> MARYLAND</td>\n",
-        "      <td> 2015</td>\n",
-        "    </tr>\n",
-        "  </tbody>\n",
-        "</table>\n",
-        "</div>"
-       ],
-       "metadata": {},
-       "output_type": "pyout",
-       "prompt_number": 5,
-       "text": [
-        "   population     state  year\n",
-        "0         5.0  VIRGINIA  2012\n",
-        "1         5.1  VIRGINIA  2013\n",
-        "2         5.2  VIRGINIA  2014\n",
-        "3         4.0  MARYLAND  2014\n",
-        "4         4.1  MARYLAND  2015"
-       ]
-      }
-     ],
-     "prompt_number": 5
-    },
-    {
-     "cell_type": "markdown",
-     "metadata": {},
-     "source": [
-      "## Drop"
-     ]
-    },
-    {
-     "cell_type": "markdown",
-     "metadata": {},
-     "source": [
-      "Drop the 'population' column and return a copy of the DataFrame:"
-     ]
-    },
-    {
-     "cell_type": "code",
-     "collapsed": false,
-     "input": [
-      "df_2 = df_1.drop('population', axis=1)\n",
-      "df_2"
-     ],
-     "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>state</th>\n",
-        "      <th>year</th>\n",
-        "    </tr>\n",
-        "  </thead>\n",
-        "  <tbody>\n",
-        "    <tr>\n",
-        "      <th>0</th>\n",
-        "      <td> VIRGINIA</td>\n",
-        "      <td> 2012</td>\n",
-        "    </tr>\n",
-        "    <tr>\n",
-        "      <th>1</th>\n",
-        "      <td> VIRGINIA</td>\n",
-        "      <td> 2013</td>\n",
-        "    </tr>\n",
-        "    <tr>\n",
-        "      <th>2</th>\n",
-        "      <td> VIRGINIA</td>\n",
-        "      <td> 2014</td>\n",
-        "    </tr>\n",
-        "    <tr>\n",
-        "      <th>3</th>\n",
-        "      <td> MARYLAND</td>\n",
-        "      <td> 2014</td>\n",
-        "    </tr>\n",
-        "    <tr>\n",
-        "      <th>4</th>\n",
-        "      <td> MARYLAND</td>\n",
-        "      <td> 2015</td>\n",
-        "    </tr>\n",
-        "  </tbody>\n",
-        "</table>\n",
-        "</div>"
-       ],
-       "metadata": {},
-       "output_type": "pyout",
-       "prompt_number": 6,
-       "text": [
-        "      state  year\n",
-        "0  VIRGINIA  2012\n",
-        "1  VIRGINIA  2013\n",
-        "2  VIRGINIA  2014\n",
-        "3  MARYLAND  2014\n",
-        "4  MARYLAND  2015"
-       ]
-      }
-     ],
-     "prompt_number": 6
-    },
-    {
-     "cell_type": "markdown",
-     "metadata": {},
-     "source": [
-      "## Concatenate"
-     ]
-    },
-    {
-     "cell_type": "markdown",
-     "metadata": {},
-     "source": [
-      "Concatenate two DataFrames:"
-     ]
-    },
-    {
-     "cell_type": "code",
-     "collapsed": false,
-     "input": [
-      "data_2 = {'state' : ['NY', 'NY', 'NY', 'FL', 'FL'],\n",
-      "          'year' : [2012, 2013, 2014, 2014, 2015],\n",
-      "          'population' : [6.0, 6.1, 6.2, 3.0, 3.1]}\n",
-      "df_3 = DataFrame(data_2)\n",
-      "df_3"
-     ],
-     "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>population</th>\n",
-        "      <th>state</th>\n",
-        "      <th>year</th>\n",
-        "    </tr>\n",
-        "  </thead>\n",
-        "  <tbody>\n",
-        "    <tr>\n",
-        "      <th>0</th>\n",
-        "      <td> 6.0</td>\n",
-        "      <td> NY</td>\n",
-        "      <td> 2012</td>\n",
-        "    </tr>\n",
-        "    <tr>\n",
-        "      <th>1</th>\n",
-        "      <td> 6.1</td>\n",
-        "      <td> NY</td>\n",
-        "      <td> 2013</td>\n",
-        "    </tr>\n",
-        "    <tr>\n",
-        "      <th>2</th>\n",
-        "      <td> 6.2</td>\n",
-        "      <td> NY</td>\n",
-        "      <td> 2014</td>\n",
-        "    </tr>\n",
-        "    <tr>\n",
-        "      <th>3</th>\n",
-        "      <td> 3.0</td>\n",
-        "      <td> FL</td>\n",
-        "      <td> 2014</td>\n",
-        "    </tr>\n",
-        "    <tr>\n",
-        "      <th>4</th>\n",
-        "      <td> 3.1</td>\n",
-        "      <td> FL</td>\n",
-        "      <td> 2015</td>\n",
-        "    </tr>\n",
-        "  </tbody>\n",
-        "</table>\n",
-        "</div>"
-       ],
-       "metadata": {},
-       "output_type": "pyout",
-       "prompt_number": 7,
-       "text": [
-        "   population state  year\n",
-        "0         6.0    NY  2012\n",
-        "1         6.1    NY  2013\n",
-        "2         6.2    NY  2014\n",
-        "3         3.0    FL  2014\n",
-        "4         3.1    FL  2015"
-       ]
-      }
-     ],
-     "prompt_number": 7
-    },
-    {
-     "cell_type": "code",
-     "collapsed": false,
-     "input": [
-      "df_4 = pd.concat([df_1, df_3])\n",
-      "df_4"
-     ],
-     "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>population</th>\n",
-        "      <th>state</th>\n",
-        "      <th>year</th>\n",
-        "    </tr>\n",
-        "  </thead>\n",
-        "  <tbody>\n",
-        "    <tr>\n",
-        "      <th>0</th>\n",
-        "      <td> 5.0</td>\n",
-        "      <td> VIRGINIA</td>\n",
-        "      <td> 2012</td>\n",
-        "    </tr>\n",
-        "    <tr>\n",
-        "      <th>1</th>\n",
-        "      <td> 5.1</td>\n",
-        "      <td> VIRGINIA</td>\n",
-        "      <td> 2013</td>\n",
-        "    </tr>\n",
-        "    <tr>\n",
-        "      <th>2</th>\n",
-        "      <td> 5.2</td>\n",
-        "      <td> VIRGINIA</td>\n",
-        "      <td> 2014</td>\n",
-        "    </tr>\n",
-        "    <tr>\n",
-        "      <th>3</th>\n",
-        "      <td> 4.0</td>\n",
-        "      <td> MARYLAND</td>\n",
-        "      <td> 2014</td>\n",
-        "    </tr>\n",
-        "    <tr>\n",
-        "      <th>4</th>\n",
-        "      <td> 4.1</td>\n",
-        "      <td> MARYLAND</td>\n",
-        "      <td> 2015</td>\n",
-        "    </tr>\n",
-        "    <tr>\n",
-        "      <th>0</th>\n",
-        "      <td> 6.0</td>\n",
-        "      <td>       NY</td>\n",
-        "      <td> 2012</td>\n",
-        "    </tr>\n",
-        "    <tr>\n",
-        "      <th>1</th>\n",
-        "      <td> 6.1</td>\n",
-        "      <td>       NY</td>\n",
-        "      <td> 2013</td>\n",
-        "    </tr>\n",
-        "    <tr>\n",
-        "      <th>2</th>\n",
-        "      <td> 6.2</td>\n",
-        "      <td>       NY</td>\n",
-        "      <td> 2014</td>\n",
-        "    </tr>\n",
-        "    <tr>\n",
-        "      <th>3</th>\n",
-        "      <td> 3.0</td>\n",
-        "      <td>       FL</td>\n",
-        "      <td> 2014</td>\n",
-        "    </tr>\n",
-        "    <tr>\n",
-        "      <th>4</th>\n",
-        "      <td> 3.1</td>\n",
-        "      <td>       FL</td>\n",
-        "      <td> 2015</td>\n",
-        "    </tr>\n",
-        "  </tbody>\n",
-        "</table>\n",
-        "</div>"
-       ],
-       "metadata": {},
-       "output_type": "pyout",
-       "prompt_number": 8,
-       "text": [
-        "   population     state  year\n",
-        "0         5.0  VIRGINIA  2012\n",
-        "1         5.1  VIRGINIA  2013\n",
-        "2         5.2  VIRGINIA  2014\n",
-        "3         4.0  MARYLAND  2014\n",
-        "4         4.1  MARYLAND  2015\n",
-        "0         6.0        NY  2012\n",
-        "1         6.1        NY  2013\n",
-        "2         6.2        NY  2014\n",
-        "3         3.0        FL  2014\n",
-        "4         3.1        FL  2015"
-       ]
-      }
-     ],
-     "prompt_number": 8
-    },
-    {
-     "cell_type": "code",
-     "collapsed": false,
-     "input": [],
-     "language": "python",
-     "metadata": {},
-     "outputs": [],
-     "prompt_number": 8
+     "output_type": "execute_result"
     }
    ],
-   "metadata": {}
+   "source": [
+    "data_1 = {'state' : ['VA', 'VA', 'VA', 'MD', 'MD'],\n",
+    "          'year' : [2012, 2013, 2014, 2014, 2015],\n",
+    "          'population' : [5.0, 5.1, 5.2, 4.0, 4.1]}\n",
+    "df_1 = DataFrame(data_1)\n",
+    "df_1"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Replace"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "Replace all occurrences of a string with another string, in place (no copy):"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 4,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [
+    {
+     "data": {
+      "text/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>population</th>\n",
+       "      <th>state</th>\n",
+       "      <th>year</th>\n",
+       "    </tr>\n",
+       "  </thead>\n",
+       "  <tbody>\n",
+       "    <tr>\n",
+       "      <th>0</th>\n",
+       "      <td> 5.0</td>\n",
+       "      <td> VIRGINIA</td>\n",
+       "      <td> 2012</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>1</th>\n",
+       "      <td> 5.1</td>\n",
+       "      <td> VIRGINIA</td>\n",
+       "      <td> 2013</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>2</th>\n",
+       "      <td> 5.2</td>\n",
+       "      <td> VIRGINIA</td>\n",
+       "      <td> 2014</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>3</th>\n",
+       "      <td> 4.0</td>\n",
+       "      <td>       MD</td>\n",
+       "      <td> 2014</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>4</th>\n",
+       "      <td> 4.1</td>\n",
+       "      <td>       MD</td>\n",
+       "      <td> 2015</td>\n",
+       "    </tr>\n",
+       "  </tbody>\n",
+       "</table>\n",
+       "</div>"
+      ],
+      "text/plain": [
+       "   population     state  year\n",
+       "0         5.0  VIRGINIA  2012\n",
+       "1         5.1  VIRGINIA  2013\n",
+       "2         5.2  VIRGINIA  2014\n",
+       "3         4.0        MD  2014\n",
+       "4         4.1        MD  2015"
+      ]
+     },
+     "execution_count": 4,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "df_1.replace('VA', 'VIRGINIA', inplace=True)\n",
+    "df_1"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "In a specified column, replace all occurrences of a string with another string, in place (no copy):"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 5,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [
+    {
+     "data": {
+      "text/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>population</th>\n",
+       "      <th>state</th>\n",
+       "      <th>year</th>\n",
+       "    </tr>\n",
+       "  </thead>\n",
+       "  <tbody>\n",
+       "    <tr>\n",
+       "      <th>0</th>\n",
+       "      <td> 5.0</td>\n",
+       "      <td> VIRGINIA</td>\n",
+       "      <td> 2012</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>1</th>\n",
+       "      <td> 5.1</td>\n",
+       "      <td> VIRGINIA</td>\n",
+       "      <td> 2013</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>2</th>\n",
+       "      <td> 5.2</td>\n",
+       "      <td> VIRGINIA</td>\n",
+       "      <td> 2014</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>3</th>\n",
+       "      <td> 4.0</td>\n",
+       "      <td> MARYLAND</td>\n",
+       "      <td> 2014</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>4</th>\n",
+       "      <td> 4.1</td>\n",
+       "      <td> MARYLAND</td>\n",
+       "      <td> 2015</td>\n",
+       "    </tr>\n",
+       "  </tbody>\n",
+       "</table>\n",
+       "</div>"
+      ],
+      "text/plain": [
+       "   population     state  year\n",
+       "0         5.0  VIRGINIA  2012\n",
+       "1         5.1  VIRGINIA  2013\n",
+       "2         5.2  VIRGINIA  2014\n",
+       "3         4.0  MARYLAND  2014\n",
+       "4         4.1  MARYLAND  2015"
+      ]
+     },
+     "execution_count": 5,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "df_1.replace({'state' : { 'MD' : 'MARYLAND' }}, inplace=True)\n",
+    "df_1"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Drop"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "Drop the 'population' column and return a copy of the DataFrame:"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 6,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [
+    {
+     "data": {
+      "text/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>state</th>\n",
+       "      <th>year</th>\n",
+       "    </tr>\n",
+       "  </thead>\n",
+       "  <tbody>\n",
+       "    <tr>\n",
+       "      <th>0</th>\n",
+       "      <td> VIRGINIA</td>\n",
+       "      <td> 2012</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>1</th>\n",
+       "      <td> VIRGINIA</td>\n",
+       "      <td> 2013</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>2</th>\n",
+       "      <td> VIRGINIA</td>\n",
+       "      <td> 2014</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>3</th>\n",
+       "      <td> MARYLAND</td>\n",
+       "      <td> 2014</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>4</th>\n",
+       "      <td> MARYLAND</td>\n",
+       "      <td> 2015</td>\n",
+       "    </tr>\n",
+       "  </tbody>\n",
+       "</table>\n",
+       "</div>"
+      ],
+      "text/plain": [
+       "      state  year\n",
+       "0  VIRGINIA  2012\n",
+       "1  VIRGINIA  2013\n",
+       "2  VIRGINIA  2014\n",
+       "3  MARYLAND  2014\n",
+       "4  MARYLAND  2015"
+      ]
+     },
+     "execution_count": 6,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "df_2 = df_1.drop('population', axis=1)\n",
+    "df_2"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Concatenate"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "Concatenate two DataFrames:"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 7,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [
+    {
+     "data": {
+      "text/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>population</th>\n",
+       "      <th>state</th>\n",
+       "      <th>year</th>\n",
+       "    </tr>\n",
+       "  </thead>\n",
+       "  <tbody>\n",
+       "    <tr>\n",
+       "      <th>0</th>\n",
+       "      <td> 6.0</td>\n",
+       "      <td> NY</td>\n",
+       "      <td> 2012</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>1</th>\n",
+       "      <td> 6.1</td>\n",
+       "      <td> NY</td>\n",
+       "      <td> 2013</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>2</th>\n",
+       "      <td> 6.2</td>\n",
+       "      <td> NY</td>\n",
+       "      <td> 2014</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>3</th>\n",
+       "      <td> 3.0</td>\n",
+       "      <td> FL</td>\n",
+       "      <td> 2014</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>4</th>\n",
+       "      <td> 3.1</td>\n",
+       "      <td> FL</td>\n",
+       "      <td> 2015</td>\n",
+       "    </tr>\n",
+       "  </tbody>\n",
+       "</table>\n",
+       "</div>"
+      ],
+      "text/plain": [
+       "   population state  year\n",
+       "0         6.0    NY  2012\n",
+       "1         6.1    NY  2013\n",
+       "2         6.2    NY  2014\n",
+       "3         3.0    FL  2014\n",
+       "4         3.1    FL  2015"
+      ]
+     },
+     "execution_count": 7,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "data_2 = {'state' : ['NY', 'NY', 'NY', 'FL', 'FL'],\n",
+    "          'year' : [2012, 2013, 2014, 2014, 2015],\n",
+    "          'population' : [6.0, 6.1, 6.2, 3.0, 3.1]}\n",
+    "df_3 = DataFrame(data_2)\n",
+    "df_3"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 8,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [
+    {
+     "data": {
+      "text/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>population</th>\n",
+       "      <th>state</th>\n",
+       "      <th>year</th>\n",
+       "    </tr>\n",
+       "  </thead>\n",
+       "  <tbody>\n",
+       "    <tr>\n",
+       "      <th>0</th>\n",
+       "      <td> 5.0</td>\n",
+       "      <td> VIRGINIA</td>\n",
+       "      <td> 2012</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>1</th>\n",
+       "      <td> 5.1</td>\n",
+       "      <td> VIRGINIA</td>\n",
+       "      <td> 2013</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>2</th>\n",
+       "      <td> 5.2</td>\n",
+       "      <td> VIRGINIA</td>\n",
+       "      <td> 2014</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>3</th>\n",
+       "      <td> 4.0</td>\n",
+       "      <td> MARYLAND</td>\n",
+       "      <td> 2014</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>4</th>\n",
+       "      <td> 4.1</td>\n",
+       "      <td> MARYLAND</td>\n",
+       "      <td> 2015</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>0</th>\n",
+       "      <td> 6.0</td>\n",
+       "      <td>       NY</td>\n",
+       "      <td> 2012</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>1</th>\n",
+       "      <td> 6.1</td>\n",
+       "      <td>       NY</td>\n",
+       "      <td> 2013</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>2</th>\n",
+       "      <td> 6.2</td>\n",
+       "      <td>       NY</td>\n",
+       "      <td> 2014</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>3</th>\n",
+       "      <td> 3.0</td>\n",
+       "      <td>       FL</td>\n",
+       "      <td> 2014</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>4</th>\n",
+       "      <td> 3.1</td>\n",
+       "      <td>       FL</td>\n",
+       "      <td> 2015</td>\n",
+       "    </tr>\n",
+       "  </tbody>\n",
+       "</table>\n",
+       "</div>"
+      ],
+      "text/plain": [
+       "   population     state  year\n",
+       "0         5.0  VIRGINIA  2012\n",
+       "1         5.1  VIRGINIA  2013\n",
+       "2         5.2  VIRGINIA  2014\n",
+       "3         4.0  MARYLAND  2014\n",
+       "4         4.1  MARYLAND  2015\n",
+       "0         6.0        NY  2012\n",
+       "1         6.1        NY  2013\n",
+       "2         6.2        NY  2014\n",
+       "3         3.0        FL  2014\n",
+       "4         3.1        FL  2015"
+      ]
+     },
+     "execution_count": 8,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "df_4 = pd.concat([df_1, df_3])\n",
+    "df_4"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 8,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [],
+   "source": []
   }
- ]
-}
\ No newline at end of file
+ ],
+ "metadata": {
+  "kernelspec": {
+   "display_name": "Python 2",
+   "language": "python",
+   "name": "python2"
+  },
+  "language_info": {
+   "codemirror_mode": {
+    "name": "ipython",
+    "version": 2
+   },
+   "file_extension": ".py",
+   "mimetype": "text/x-python",
+   "name": "python",
+   "nbconvert_exporter": "python",
+   "pygments_lexer": "ipython2",
+   "version": "2.7.9"
+  }
+ },
+ "nbformat": 4,
+ "nbformat_minor": 0
+}