Chapter 5 - Writing Fast Code.ipynb

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     "source": [
      "Vectorize\n",
      "============"
     ]
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     "cell_type": "code",
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     "input": [
      "import numpy as np\n",
      "a = np.random.uniform(size=10000)\n",
      "b = np.random.uniform(size=10000)\n",
      "%time c = a + b\n"
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     "language": "python",
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     "input": [
      "def add_vectors(first, second):\n",
      "    a = np.empty(first.shape)\n",
      "    for i in xrange(len(first)):\n",
      "        a[i] = first[i] + second[i]\n",
      "        "
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     "input": [
      "%time c = add_vectors(a, b)"
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     "source": [
      "Don't write for-loops!\n",
      "------------------------\n",
      "\n",
      "If you can't avoid it (writing your custom algorithms)\n",
      "Use Cython\n",
      "==========="
     ]
    },
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     "cell_type": "code",
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     "input": [
      "%load_ext cythonmagic"
     ],
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     "input": [
      "%%cython\n",
      "\n",
      "import numpy as np\n",
      "cimport numpy as np\n",
      "\n",
      "def add_vectors_fast(first, second):\n",
      "    a = np.empty(first.shape)\n",
      "    for i in xrange(len(first)):\n",
      "        a[i] = first[i] + second[i]\n",
      "    return a\n"
     ],
     "language": "python",
     "metadata": {},
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     "cell_type": "code",
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     "input": [
      "%time c = add_vectors_fast(a, b)"
     ],
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     "input": [
      "%%cython\n",
      "\n",
      "cimport cython\n",
      "cimport numpy as np\n",
      "\n",
      "#@cython.boundscheck(False)\n",
      "#@cython.wraparound(False)\n",
      "def add_vectors_fast2(double[:] first, double[:] second):\n",
      "    cdef np.ndarray[double, ndim = 1, mode = \"c\"] a = np.ndarray(first.shape[0])\n",
      "    #cdef int i\n",
      "    for i in range(len(first)):\n",
      "        a[i] = first[i] + second[i]\n",
      "    return a\n"
     ],
     "language": "python",
     "metadata": {},
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     "cell_type": "code",
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     "input": [
      "%time c = add_vectors_fast2(a, b)"
     ],
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