python/Get the first element after split.ipynb

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   "source": [
    "### Get the first element after split"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "`str.split` finds all the occurrences of a separator and returns a list.\n",
    "\n",
    "If you only need the first element then this is inefficient in two ways:\n",
    "- There's search for the separator beyond the first occurrence\n",
    "- The method returns all the other elements in the last which is not needed"
   ]
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   "metadata": {
    "collapsed": true
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   "source": [
    "def get_first_split(input_string, split_by=' '):\n",
    "    try:\n",
    "        input_string_stripped = input_string.strip()\n",
    "        split_by_index = input_string_stripped.find(split_by)\n",
    "        if split_by_index == -1:\n",
    "            return input_string_stripped\n",
    "        else:\n",
    "            substring = input_string_stripped[:split_by_index].strip()\n",
    "            return substring\n",
    "    except AttributeError:\n",
    "        return ''"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "'this is'"
      ]
     },
     "execution_count": 2,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "get_first_split(' this is  _ a test', '_')"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "metadata": {
    "collapsed": false
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   "outputs": [
    {
     "data": {
      "text/plain": [
       "'some'"
      ]
     },
     "execution_count": 3,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "get_first_split('some_group_1', '_')"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### Performance compared to `str.split`"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 8,
   "metadata": {
    "collapsed": false
   },
   "outputs": [],
   "source": [
    "x = 'XQWRQW' * 100000\n",
    "x += ' ' + ('XWQQWFW' * 100000)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 9,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "1300001"
      ]
     },
     "execution_count": 9,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "len(x)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 46,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "1000 loops, best of 3: 1.43 ms per loop\n"
     ]
    }
   ],
   "source": [
    "%%timeit\n",
    "x.split()[0]"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 12,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "1000 loops, best of 3: 700 µs per loop\n"
     ]
    }
   ],
   "source": [
    "%%timeit\n",
    "x.split(maxsplit=1)[0]"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 47,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "10000 loops, best of 3: 53.4 µs per loop\n"
     ]
    }
   ],
   "source": [
    "%%timeit\n",
    "get_first_split(x)"
   ]
  }
 ],
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