Merge pull request #44 from silverriver/silver_dev

typo in 59 and changed solution of 66

100 Numpy exercises no solution.ipynb

@@ -1015,7 +1015,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "#### 59. How to I sort an array by the nth column? (★★☆)"
+    "#### 59. How to sort an array by the nth column? (★★☆)"
    ]
   },
   {

100 Numpy exercises.ipynb

@@ -1243,7 +1243,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "#### 59. How to I sort an array by the nth column? (★★☆)"
+    "#### 59. How to sort an array by the nth column? (★★☆)"
    ]
   },
   {
@@ -1423,9 +1423,11 @@
     "\n",
     "w,h = 16,16\n",
     "I = np.random.randint(0,2,(h,w,3)).astype(np.ubyte)\n",
-    "F = I[...,0]*256*256 + I[...,1]*256 +I[...,2]\n",
+    "#Note that we should compute 256*256 first. \n",
+    "#Otherwise numpy will only promote F.dtype to 'uint16' and overfolw will occur\n",
+    "F = I[...,0]*(256*256) + I[...,1]*256 +I[...,2]\n",
     "n = len(np.unique(F))\n",
-    "print(np.unique(I))"
+    "print(n)"
    ]
   },
   {