{
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   "source": [
    "# Optional Lab: Linear Regression using Scikit-Learn"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "There is an open-source, commercially usable machine learning toolkit called [scikit-learn](https://scikit-learn.org/stable/index.html). This toolkit contains implementations of many of the algorithms that you will work with in this course.\n",
    "\n"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Goals\n",
    "In this lab you will:\n",
    "- Utilize  scikit-learn to implement linear regression using a close form solution based on the normal equation"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Tools\n",
    "You will utilize functions from scikit-learn as well as matplotlib and NumPy. "
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "import numpy as np\n",
    "import matplotlib.pyplot as plt\n",
    "from sklearn.linear_model import LinearRegression\n",
    "from lab_utils_multi import load_house_data\n",
    "plt.style.use('./deeplearning.mplstyle')\n",
    "np.set_printoptions(precision=2)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "<a name=\"toc_40291_2\"></a>\n",
    "# Linear Regression, closed-form solution\n",
    "Scikit-learn has the [linear regression model](https://scikit-learn.org/stable/modules/generated/sklearn.linear_model.LinearRegression.html#sklearn.linear_model.LinearRegression) which implements a closed-form linear regression.\n",
    "\n",
    "Let's use the data from the early labs - a house with 1000 square feet sold for \\\\$300,000 and a house with 2000 square feet sold for \\\\$500,000.\n",
    "\n",
    "| Size (1000 sqft)     | Price (1000s of dollars) |\n",
    "| ----------------| ------------------------ |\n",
    "| 1               | 300                      |\n",
    "| 2               | 500                      |\n"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### Load the data set"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "X_train = np.array([1.0, 2.0])   #features\n",
    "y_train = np.array([300, 500])   #target value"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### Create and fit the model\n",
    "The code below performs regression using scikit-learn. \n",
    "The first step creates a regression object.  \n",
    "The second step utilizes one of the methods associated with the object, `fit`. This performs regression, fitting the parameters to the input data. The toolkit expects a two-dimensional X matrix."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "linear_model = LinearRegression()\n",
    "#X must be a 2-D Matrix\n",
    "linear_model.fit(X_train.reshape(-1, 1), y_train) "
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### View Parameters \n",
    "The $\\mathbf{w}$ and $\\mathbf{b}$ parameters are referred to as 'coefficients' and 'intercept' in scikit-learn."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "b = linear_model.intercept_\n",
    "w = linear_model.coef_\n",
    "print(f\"w = {w:}, b = {b:0.2f}\")\n",
    "print(f\"'manual' prediction: f_wb = wx+b : {1200*w + b}\")"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### Make Predictions\n",
    "\n",
    "Calling the `predict` function generates predictions."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "y_pred = linear_model.predict(X_train.reshape(-1, 1))\n",
    "\n",
    "print(\"Prediction on training set:\", y_pred)\n",
    "\n",
    "X_test = np.array([[1200]])\n",
    "print(f\"Prediction for 1200 sqft house: ${linear_model.predict(X_test)[0]:0.2f}\")"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Second Example\n",
    "The second example is from an earlier lab with multiple features. The final parameter values and predictions are very close to the results from the un-normalized 'long-run' from that lab. That un-normalized run took hours to produce results, while this is nearly instantaneous. The closed-form solution work well on smaller data sets such as these but can be computationally demanding on larger data sets. \n",
    ">The closed-form solution does not require normalization."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "# load the dataset\n",
    "X_train, y_train = load_house_data()\n",
    "X_features = ['size(sqft)','bedrooms','floors','age']"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "linear_model = LinearRegression()\n",
    "linear_model.fit(X_train, y_train) "
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "b = linear_model.intercept_\n",
    "w = linear_model.coef_\n",
    "print(f\"w = {w:}, b = {b:0.2f}\")"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "print(f\"Prediction on training set:\\n {linear_model.predict(X_train)[:4]}\" )\n",
    "print(f\"prediction using w,b:\\n {(X_train @ w + b)[:4]}\")\n",
    "print(f\"Target values \\n {y_train[:4]}\")\n",
    "\n",
    "x_house = np.array([1200, 3,1, 40]).reshape(-1,4)\n",
    "x_house_predict = linear_model.predict(x_house)[0]\n",
    "print(f\" predicted price of a house with 1200 sqft, 3 bedrooms, 1 floor, 40 years old = ${x_house_predict*1000:0.2f}\")"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Congratulations!\n",
    "In this lab you:\n",
    "- utilized an open-source machine learning toolkit, scikit-learn\n",
    "- implemented linear regression using a close-form solution from that toolkit"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": []
  }
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