Indexing a 2D NumPy array to sample a map

Sampling map by indexing.ipynb

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  {
   "cell_type": "markdown",
   "id": "5322c8a6",
   "metadata": {},
   "source": [
    "# Get samples from a NumPy array with coordinates\n",
    "\n",
    "Let's say we have a map, as a 2D array, and some coordinates (pairs of x, y index locations).\n",
    "\n",
    "I'd like to sample the map (below) at those locations (the white dots)."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "id": "3da14026",
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "<matplotlib.collections.PathCollection at 0x7fa7b090ad90>"
      ]
     },
     "execution_count": 1,
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      "text/plain": [
       "<Figure size 432x288 with 1 Axes>"
      ]
     },
     "metadata": {
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     "output_type": "display_data"
    }
   ],
   "source": [
    "import numpy as np\n",
    "import matplotlib.pyplot as plt\n",
    "\n",
    "arr = np.arange(25).reshape(5, 5)\n",
    "pos = np.array([(0, 0), (2, 3), (4, 1), (4, 4)])\n",
    "\n",
    "plt.imshow(arr)\n",
    "plt.scatter(*pos.T, c='w')"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "9133d33d",
   "metadata": {},
   "source": [
    "Get those samples with indexing"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "id": "3659abf9",
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "array([ 0, 13, 21, 24])"
      ]
     },
     "execution_count": 2,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "arr[tuple(pos.T)]"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "017ca20b",
   "metadata": {},
   "source": [
    "---\n",
    "\n",
    "© Agile Scientific CC BY"
   ]
  }
 ],
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