array_indexing.ipynb

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  {
   "cell_type": "markdown",
   "id": "7451d6a1",
   "metadata": {},
   "source": [
    "# Array indexing exercise\n",
    "\n",
    "These exercises follow on from the [array indexing page](https://lisds.github.io/textbook/arrays/array_indexing), and the page on [Boolean arrays]( https://lisds.github.io/textbook/arrays/boolean_arrays)."
   ]
  },
  {
   "cell_type": "markdown",
   "id": "b32fc170",
   "metadata": {},
   "source": [
    "Run this cell to start:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "f6ecfc58",
   "metadata": {},
   "outputs": [],
   "source": [
    "# Don't change this cell; just run it.\n",
    "import numpy as np\n",
    "\n",
    "# The OKpy testing system.\n",
    "from client.api.notebook import Notebook\n",
    "ok = Notebook('array_indexing.ok')"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "597c5408",
   "metadata": {},
   "source": [
    "Here is the beginning of Hamlet's famous speech:\n",
    "\n",
    "> To be, or not to be, that is the question:\n",
    "> Whether 'tis nobler in the mind to suffer\n",
    "> The slings and arrows of outrageous fortune,\n",
    "\n",
    "And here is a slightly wrong version, as an array of words, and without the punctuation:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "b7911398",
   "metadata": {},
   "outputs": [],
   "source": [
    "# A quote that isn't quite right.\n",
    "hamlets_words = np.array(['to', 'be', 'or', 'not', 'to', 'be',\n",
    "                          'that', 'be', 'the', 'question',\n",
    "                          'whether', 'be', 'nobler', 'in', 'the', 'marrow',\n",
    "                          'to', 'suffer', 'the', 'slings', 'and', 'arrows',\n",
    "                          'of', 'outrageous', 'fortune'])\n",
    "hamlets_words"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "34265235",
   "metadata": {},
   "source": [
    "We can use the `join` method of strings to join these words together with a space (\" \") between each word:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "8eb2afa7",
   "metadata": {},
   "outputs": [],
   "source": [
    "\" \".join(hamlets_words)"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "15758e23",
   "metadata": {},
   "source": [
    "## Indexing with integers\n",
    "\n",
    "Use indexing with integers to set `first_word` to contain the first word in\n",
    "`hamlets_words`."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "34507a64",
   "metadata": {},
   "outputs": [],
   "source": [
    "first_word = ...\n",
    "first_word"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "9c3bb512",
   "metadata": {},
   "source": [
    "Test the result:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "f00f9c9b",
   "metadata": {},
   "outputs": [],
   "source": [
    "_ = ok.grade('q_first_word')"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "7cfe55b3",
   "metadata": {},
   "source": [
    "Use indexing with integers to set `funny_word` to have the value \"marrow\"."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "2480ac6d",
   "metadata": {},
   "outputs": [],
   "source": [
    "funny_word = ...\n",
    "funny_word"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "979864b2",
   "metadata": {},
   "source": [
    "Test the result:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "d4178f7d",
   "metadata": {},
   "outputs": [],
   "source": [
    "_ = ok.grade('q_funny_word')"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "6526361b",
   "metadata": {},
   "source": [
    "Make a Boolean array `bees` that has `True` where the word in the matching\n",
    "position of `hamlets_words` is \"be\":"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "24b48c6e",
   "metadata": {},
   "outputs": [],
   "source": [
    "bees = hamlets_words...\n",
    "bees"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "d3973a5b",
   "metadata": {},
   "outputs": [],
   "source": [
    "_ = ok.grade('q_bees')"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "1ded0316",
   "metadata": {},
   "source": [
    "Use `np.count_nonzero` to set `n_bees` to have the number of times the word \"be\" appears in `hamlets_words`."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "5a244a06",
   "metadata": {},
   "outputs": [],
   "source": [
    "n_bees = ...\n",
    "n_bees"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "1fced47f",
   "metadata": {},
   "outputs": [],
   "source": [
    "_ = ok.grade('q_n_bees')"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "ae931af9",
   "metadata": {},
   "source": [
    "Run this cell to make a copy of `hamlets_words`. This uses the `copy` method of the array, to return a new copy."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "7fa66c1e",
   "metadata": {},
   "outputs": [],
   "source": [
    "# Run this cell\n",
    "hamlet_improved = hamlets_words.copy()"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "6337d6df",
   "metadata": {},
   "source": [
    "Use array assignment with indexing, to replace the word \"marrow\" with the world \"mind\", in the `hamlet_improved` array"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "c9e167ee",
   "metadata": {},
   "outputs": [],
   "source": [
    "hamlet_improved[.....\n",
    "hamlet_improved"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "2cc8d29c",
   "metadata": {},
   "outputs": [],
   "source": [
    "_ = ok.grade('q_hamlet_improved')"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "9bebe2f8",
   "metadata": {},
   "source": [
    "Run this cell to make a copy of `hamlet_improved` to finish up your work of fixing."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "bc8d1ec0",
   "metadata": {},
   "outputs": [],
   "source": [
    "# Run this cell\n",
    "hamlet_fixed = hamlet_improved.copy()"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "2a66149f",
   "metadata": {},
   "source": [
    "Use array assignment with indexing to fix the remaining words in the\n",
    "`hamlet_fixed` quote, and then set `hamlet_joined` to the result of joining\n",
    "the words with a space.\n",
    "\n",
    "You will likely need a few lines here."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "d349a983",
   "metadata": {},
   "outputs": [],
   "source": [
    "hamlet_fixed[...\n",
    "...\n",
    "hamlet_joined = ...\n",
    "hamlet_joined"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "9eb0c13b",
   "metadata": {},
   "outputs": [],
   "source": [
    "_ = ok.grade('q_hamlet_joined')"
   ]
  }
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