Refactor solutions for Acitvities 3-4, of Part 2 of Chapter 0.

Author: UPstartDeveloper

chapter0-exercises/chapter_0_part2.ipynb

@@ -256,11 +256,11 @@
         "    numbers = nums.copy()\n",
         "    # B: mark the duplicates\n",
         "    for index in range(len(nums)):\n",
-        "        # if this number appears again, then it's a duplicate\n",
+        "        # C: if this number appears again, then it's a duplicate\n",
         "        rest_of_list = numbers[index+1:]\n",
         "        if numbers[index] in rest_of_list:\n",
         "            numbers[index] = 0  \n",
-        "    # C: return all non-duplicates\n",
+        "    # D: return all non-duplicates\n",
         "    return [num for num in numbers if num != 0]\n",
         "\n",
         "print(remove_duplicates_3(nums))"
@@ -283,8 +283,8 @@
         "id": "DjhcUMXvw8sB"
       },
       "source": [
-        "# TODO: explain above that this solution is just like above, except we instead\n",
-        "    # just delete the duplicate values from the list "
+        "TODO: explain above that this solution is just like above, except we instead\n",
+        "    # just delete the duplicate values from the list"
       ],
       "id": "DjhcUMXvw8sB"
     },
@@ -309,13 +309,13 @@
         "    while num_checks < original_length:\n",
         "        num_checks += 1\n",
         "        rest_of_list = numbers[index+1:]\n",
-        "        # duplicate found\n",
+        "        # C: duplicate found\n",
         "        if numbers[index] in rest_of_list:\n",
         "            del numbers[index]\n",
-        "        # duplicate not found, so move on to the next indx\n",
+        "        # D: duplicate not found, so move on to the next indx\n",
         "        else:\n",
         "            index += 1\n",
-        "    # C: return only the non-duplicate numbers\n",
+        "    # E: return only the non-duplicate numbers\n",
         "    return numbers\n",
         "\n",
         "print(remove_duplicates_4(nums))"
@@ -386,6 +386,11 @@
       },
       "source": [
         "## Activity: Combine dictionaries\n",
+        "\n",
+        "TODO: \n",
+        "  1. mention that if there are any keys in the second that are already present in the first, then place the corresponding values together into a list, and make that the new value in the first\n",
+        "  2. again, both the input dictionaries are immutable \n",
+        "\n",
         "- d1 = {'a':10, 'b':20, 'c':30}\n",
         "- d2 = {'b': 40, 'd':50}\n",
         "- return d = {'a': 10, 'b': [20, 40], 'c': 50, 'd': 50}"
@@ -395,26 +400,34 @@
     {
       "cell_type": "code",
       "metadata": {
+        "colab": {
+          "base_uri": "https://localhost:8080/"
+        },
         "id": "sized-congo",
-        "outputId": "6267b2fe-fd5b-4f7b-9cdf-1e2cc70ac0cd"
+        "outputId": "a2a26d41-f993-4d08-8595-aceaa1a570b6"
       },
       "source": [
         "def combine_dicts(d1, d2):\n",
-        "    d = d1.copy()\n",
-        "    for key_d2,value_d2 in d2.items():\n",
-        "        if key_d2 in d:\n",
-        "            ls = d[key_d2]\n",
-        "            d[key_d2] = [ls, value_d2]\n",
+        "    # A: init a third dict\n",
+        "    combined = d1.copy()\n",
+        "    # B: add the key-value pairs from the second \n",
+        "    for key_d2, value_d2 in d2.items():\n",
+        "        # C: if an value has already been mapped to this key, include both\n",
+        "        if key_d2 in combined:\n",
+        "            value_d1 = d1[key_d2]\n",
+        "            combined[key_d2] = [value_d1, value_d2]\n",
+        "        # D: otherwise, just add the key-value pair\n",
         "        else:\n",
-        "            d[key_d2] = value_d2\n",
-        "    return d\n",
+        "            combined[key_d2] = value_d2\n",
+        "    # E: return the new dict\n",
+        "    return combined\n",
         "\n",
         "d1 = {'a':10, 'b':20, 'c':30}\n",
         "d2 = {'b': 40, 'd':50}\n",
         "print(combine_dicts(d1, d2))"
       ],
       "id": "sized-congo",
-      "execution_count": null,
+      "execution_count": 40,
       "outputs": [
         {
           "output_type": "stream",
@@ -431,30 +444,38 @@
         "id": "equal-shock"
       },
       "source": [
-        "## Activity: Flatten the given matrix"
+        "## Activity: Flatten the given matrix\n",
+        "\n",
+        "TODO: explain that this means to collect all the elements into a 1D array - they should be in the same order as on would see if your were reading the matrix row-wise"
       ],
       "id": "equal-shock"
     },
     {
       "cell_type": "code",
       "metadata": {
+        "colab": {
+          "base_uri": "https://localhost:8080/"
+        },
         "id": "soviet-accused",
-        "outputId": "b24ecf65-3c45-4752-9c3c-c2c7d65da036"
+        "outputId": "8dcdf69b-d515-4973-c1ec-bd6eb1bcd8d9"
       },
       "source": [
         "matrix = [[8, 2, 3], [9, 1, 9], [5, 4, 1]]\n",
         "\n",
-        "def flatten(matx):\n",
+        "def flatten(matrix):\n",
+        "    # A: init the 1-dimensional array\n",
         "    ls = []\n",
+        "    # B: add all the elements to it row-wise\n",
         "    for row in matrix:\n",
         "        for element in row:\n",
         "            ls.append(element)\n",
+        "    # C: return the populated list\n",
         "    return ls\n",
         "\n",
         "print(flatten(matrix))"
       ],
       "id": "soviet-accused",
-      "execution_count": null,
+      "execution_count": 42,
       "outputs": [
         {
           "output_type": "stream",
@@ -465,13 +486,42 @@
         }
       ]
     },
+    {
+      "cell_type": "markdown",
+      "metadata": {
+        "id": "o-kKYzZc7EBl"
+      },
+      "source": [
+        "TODO: show how to do the same as above, using the list.extend method"
+      ],
+      "id": "o-kKYzZc7EBl"
+    },
+    {
+      "cell_type": "code",
+      "metadata": {
+        "id": "UE1OKdqT5w1Z"
+      },
+      "source": [
+        "def flatten(matrix):\n",
+        "    # A: init the 1-dimensional array\n",
+        "    row_vector = []\n",
+        "    # B: like before, add all the elements\n",
+        "    for row in matrix:\n",
+        "        row_vector.extend(row)\n",
+        "    # C: return the populated list\n",
+        "    return row_vector"
+      ],
+      "id": "UE1OKdqT5w1Z",
+      "execution_count": 43,
+      "outputs": []
+    },
     {
       "cell_type": "markdown",
       "metadata": {
         "id": "radio-pencil"
       },
       "source": [
-        "## Activity: Obtain the trace of a given squared matrix"
+        "## Activity: Obtain the trace of a given square matrix"
       ],
       "id": "radio-pencil"
     },