matrices v2

exercises/matrices/matrices-solution.ipynb

@@ -81,13 +81,76 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 5,
+   "execution_count": 14,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "def extract_row(mat, i):\n",
+    "    \"\"\" RETURN the ith row from mat. NOTE: the row MUST be a new list ! \"\"\"\n",
+    "    #jupman-raise\n",
+    "    return mat[i][:]\n",
+    "    #/jupman-raise\n",
+    "    \n",
+    "m = [\n",
+    "      ['a','b'],\n",
+    "      ['c','d'],\n",
+    "      ['a','e'],    \n",
+    "]\n",
+    "\n",
+    "\n",
+    "r = extract_row(m, 0)\n",
+    "assert r == ['a','b']\n",
+    "r[0] = 'z'\n",
+    "r = extract_row(m, 0)\n",
+    "assert r == ['a','b']\n",
+    "\n",
+    "assert extract_row(m, 1) == ['c','d']\n",
+    "assert extract_row(m, 2) == ['a','e']\n"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 15,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "def extract_col(mat, j):\n",
+    "    \"\"\" RETURN the jth column from mat.  \"\"\"\n",
+    "    \n",
+    "    #jupman-raise\n",
+    "    ret = []\n",
+    "    \n",
+    "    for row in mat:\n",
+    "        ret.append(row[j])\n",
+    "    return ret\n",
+    "    #/jupman-raise\n",
+    "\n",
+    "m = [\n",
+    "      ['a','b'],\n",
+    "      ['c','d'],\n",
+    "      ['a','e'],    \n",
+    "]\n",
+    "\n",
+    "\n",
+    "c = extract_col(m, 0)\n",
+    "assert c == ['a','c','a']\n",
+    "c[0] = 'z'\n",
+    "c = extract_col(m, 0)\n",
+    "assert c == ['a','c','a']\n",
+    "\n",
+    "assert extract_col(m, 1) == ['b','d','e']\n",
+    "\n"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 16,
    "metadata": {},
    "outputs": [],
    "source": [
     "\n",
     "def stitch_right(mat1,mat2):\n",
-    "    \"\"\"Given matrices as list of lists mat1 of size n x l and mat2 of size n x r \n",
+    "    \"\"\"Given matrices mat1 and mat2  as list of lists, with mat1 of size n x l and mat2 of size n x r, \n",
     "       RETURN a NEW matrix of size n x (l + r) as list of lists, by stitching second mat to the right end of mat1\n",
     "    \"\"\"\n",
     "    #jupman-raise\n",
@@ -108,7 +171,7 @@
     "        ['d','b','a']\n",
     "     ]\n",
     "m2 = [\n",
-    "        [ 'f','b'],\n",
+    "        ['f','b'],\n",
     "        ['g','h']\n",
     "     ]\n",
     "\n",
@@ -120,6 +183,30 @@
     "assert stitch_right(m1, m2) == res"
    ]
   },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "Others:\n",
+    "\n",
+    "```\n",
+    "stitch_left\n",
+    "\n",
+    "mat2 mat1\n",
+    "\n",
+    "stitch_up \n",
+    "\n",
+    "mat2 \n",
+    "mat1\n",
+    "\n",
+    "stitch  down\n",
+    "\n",
+    "mat1\n",
+    "mat2\n",
+    "```\n",
+    "\n"
+   ]
+  },
   {
    "cell_type": "code",
    "execution_count": null,