03. numpy/03.09 data to & from string.ipynb

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   "source": [
    "# 数组与字符串的转换"
   ]
  },
  {
   "cell_type": "markdown",
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   "source": [
    "## tostring 方法"
   ]
  },
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   "source": [
    "import numpy as np"
   ]
  },
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   "source": [
    "a = np.array([[1,2],\n",
    "           [3,4]], \n",
    "          dtype = np.uint8)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "转化为字符串："
   ]
  },
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   "outputs": [
    {
     "data": {
      "text/plain": [
       "'\\x01\\x02\\x03\\x04'"
      ]
     },
     "execution_count": 3,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "a.tostring()"
   ]
  },
  {
   "cell_type": "markdown",
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   "source": [
    "我们可以使用不同的顺序来转换字符串："
   ]
  },
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   "execution_count": 4,
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     "data": {
      "text/plain": [
       "'\\x01\\x03\\x02\\x04'"
      ]
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     "execution_count": 4,
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   ],
   "source": [
    "a.tostring(order='F')"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "这里使用了**Fortran**的格式，按照列来读数据。"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## fromstring 函数"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "可以使用 `fromstring` 函数从字符串中读出数据，不过要指定类型："
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 5,
   "metadata": {
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   "outputs": [
    {
     "data": {
      "text/plain": [
       "array([1, 2, 3, 4], dtype=uint8)"
      ]
     },
     "execution_count": 5,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "s = a.tostring()\n",
    "a = np.fromstring(s, \n",
    "                  dtype=np.uint8)\n",
    "a"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "此时，返回的数组是一维的，需要重新设定维度："
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 6,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "array([[1, 2],\n",
       "       [3, 4]], dtype=uint8)"
      ]
     },
     "execution_count": 6,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "a.shape = 2,2\n",
    "a"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "对于文本文件，推荐使用\n",
    "- `loadtxt`\n",
    "- `genfromtxt`\n",
    "- `savetxt`\n",
    "\n",
    "对于二进制文本文件，推荐使用 \n",
    "- `save` \n",
    "- `load`\n",
    "- `savez`"
   ]
  }
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