add alternative solution to exercise 64

Author: Bartosz Telenczuk

100 Numpy exercises.ipynb

@@ -6,10 +6,10 @@
    "source": [
     "# 100 numpy exercises\n",
     "\n",
-    "This is a collection of exercises that have been collected in the numpy mailing list, on stack overflow and in the numpy documentation. I've also created some to reach the 100 limit. The goal of this collection is to offer a quick reference for both old and new users but also to provide a set of exercices for those who teach.\n",
+    "This is a collection of exercises that have been collected in the numpy mailing list, on stack overflow and in the numpy documentation. The goal of this collection is to offer a quick reference for both old and new users but also to provide a set of exercices for those who teach.\n",
     "\n",
     "\n",
-    "If you find an error or think you've a better way to solve some of them, feel free top open an issue at <https://github.com/rougier/numpy-100>"
+    "If you find an error or think you've a better way to solve some of them, feel free to open an issue at <https://github.com/rougier/numpy-100>"
    ]
   },
   {
@@ -1359,6 +1359,11 @@
     "Z = np.ones(10)\n",
     "I = np.random.randint(0,len(Z),20)\n",
     "Z += np.bincount(I, minlength=len(Z))\n",
+    "print(Z)\n",
+    "\n",
+    "# Another solution\n",
+    "# Author: Bartosz Telenczuk\n",
+    "np.add.at(Z, I, 1)\n",
     "print(Z)"
    ]
   },

100 Numpy exercises.md

@@ -1,14 +1,10 @@
 
 # 100 numpy exercises
 
-This is a collection of exercises that have been collected in the numpy mailing
-list, on stack overflow and in the numpy documentation. I've also created some
-to reach the 100 limit. The goal of this collection is to offer a quick
-reference for both old and new users but also to provide a set of exercices for
-those who teach.
+This is a collection of exercises that have been collected in the numpy mailing list, on stack overflow and in the numpy documentation. The goal of this collection is to offer a quick reference for both old and new users but also to provide a set of exercices for those who teach.
 
-If you find an error or think you've a better way to solve some of them, feel
-free to open an issue at <https://github.com/rougier/numpy-100>
+
+If you find an error or think you've a better way to solve some of them, feel free to open an issue at <https://github.com/rougier/numpy-100>
 
 #### 1. Import the numpy package under the name `np` (★☆☆)
 
@@ -43,7 +39,10 @@ print("%d bytes" % (Z.size * Z.itemsize))
 
 #### 5.  How to get the documentation of the numpy add function from the command line? (★☆☆)
 
-$ `python -c "import numpy; numpy.info(numpy.add)"`
+
+```python
+%run `python -c "import numpy; numpy.info(numpy.add)"`
+```
 
 #### 6.  Create a null vector of size 10 but the fifth value which is 1 (★☆☆)
 
@@ -651,6 +650,11 @@ Z = np.ones(10)
 I = np.random.randint(0,len(Z),20)
 Z += np.bincount(I, minlength=len(Z))
 print(Z)
+
+# Another solution
+# Author: Bartosz Telenczuk
+np.add.at(Z, I, 1)
+print(Z)
 ```
 
 #### 65. How to accumulate elements of a vector (X) to an array (F) based on an index list (I)? (★★★)