2024-heraklion-data/exercises/numpy_broadcasting_extra/broadcasting.ipynb

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    "import numpy as np\n",
    "\n",
    "def print_info(a):\n",
    "    \"\"\" Print the content of an array, and its metadata. \"\"\"\n",
    "    \n",
    "    txt = f\"\"\"\n",
    "dtype\\t{a.dtype}\n",
    "ndim\\t{a.ndim}\n",
    "shape\\t{a.shape}\n",
    "strides\\t{a.strides}\n",
    "    \"\"\"\n",
    "\n",
    "    print(a)\n",
    "    print(txt)"
   ]
  },
  {
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   "source": [
    "<font size=9> Mind-on exercises </font>"
   ]
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   "source": [
    "### Exercise 1: warm up\n",
    "\n",
    "```What is the expected output shape for each operation?```"
   ]
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   "source": [
    "a = np.arange(5)\n",
    "b = 5\n",
    "\n",
    "np.shape(a-b)"
   ]
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   "source": [
    "a = np.ones((7, 1))\n",
    "b = np.arange(7)\n",
    "np.shape(a*b)"
   ]
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   "source": [
    "a = np.random.randint(0, 50, (2, 3, 3))\n",
    "b = np.random.randint(0, 10, (3, 1))\n",
    "\n",
    "np.shape(a-b)"
   ]
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   "outputs": [],
   "source": [
    "a = np.arange(100).reshape(10, 10)\n",
    "b = np.arange(1, 10)\n",
    "\n",
    "np.shape(a+b)"
   ]
  },
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   "source": [
    "### Exercise 2\n",
    "\n",
    "```\n",
    "1. Create a random 2D array of dimension (5, 3)\n",
    "2. Calculate the maximum value of each row\n",
    "3. Divide each row by its maximum\n",
    "```\n",
    "\n",
    "Remember to use broadcasting : NO FOR LOOPS!"
   ]
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   "outputs": [],
   "source": [
    "## Your code here"
   ]
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   "source": [
    "### Exercise 3"
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   "source": [
    "Task: Find the closest **cluster** to the **observation**. \n",
    "\n",
    "Again, use broadcasting: DO NOT iterate cluster by cluster"
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    "observation = np.array([30.0, 99.0]) #Observation\n",
    "\n",
    "#Clusters\n",
    "clusters = np.array([[102.0, 203.0],\n",
    "             [132.0, 193.0],\n",
    "            [45.0, 155.0], \n",
    "            [57.0, 173.0]])"
   ]
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   "source": [
    "Lets plot this data\n",
    "\n",
    "In the plot below, **+** is the observation and dots are the cluster coordinates"
   ]
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    "import matplotlib.pyplot as plt \n",
    "\n",
    "plt.scatter(clusters[:, 0], clusters[:, 1]) #Scatter plot of clusters\n",
    "for n, x in enumerate(clusters):\n",
    "    print('cluster %d' %n)\n",
    "    plt.annotate('cluster%d' %n, (x[0], x[1])) #Label each cluster\n",
    "plt.plot(observation[0], observation[1], '+'); #Plot observation"
   ]
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    "Closest cluster as seen by the plot is **2**. Your task is to write a function to calculate this"
   ]
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   "source": [
    "\n",
    "**hint:** Find the distance between the observation and each row in the cluster. The cluster to which the observation belongs to is the row with the minimum distance.\n",
    "\n",
    "distance = $\\sqrt {\\left( {x_1 - x_2 } \\right)^2 + \\left( {y_1 - y_2 } \\right)^2 }$"
   ]
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   "outputs": [],
   "source": [
    "## Your code here"
   ]
  },
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   "source": [
    "## Sources + Resources\n",
    "\n",
    "ASPP 2016 - Stéfan van der Walt - https://github.com/ASPP/2016_numpy\n",
    "\n",
    "Basic Numpy: http://scipy-lectures.org/intro/numpy/index.html\n",
    "\n",
    "Advanced Numpy: http://scipy-lectures.org/advanced/advanced_numpy/index.html\n",
    "\n",
    "Numpy chapter in \"Python Data Science Handbook\" https://jakevdp.github.io/PythonDataScienceHandbook/02.00-introduction-to-numpy.html"
   ]
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