Merge pull request #954 from kris-joseph/gh-pages

Updated nested list example in episode 4

Author: noatgnu

_episodes/04-lists.md

@@ -166,57 +166,80 @@ does not.
 > ## Nested Lists
 > Since a list can contain any Python variables, it can even contain other lists.
 >
-> For example, we could represent the products in the shelves of a small grocery shop:
+> For example, you could represent the products on the shelves of a small grocery shop
+> as a nested list called `veg`:
+>
+> ![`veg` is represented as a shelf full of produce. There are three rows of vegetables
+> on the shelf, and each row contains three baskets of vegetables. We can label
+> each basket according to the type of vegetable it contains, so the top row
+> contains (from left to right) lettuce, lettuce, and peppers.](../fig/04_groceries_veg.png)
+>
+> To store the contents of the shelf in a nested list, you write it this way:
 >
 > ~~~
-> x = [['pepper', 'zucchini', 'onion'],
->      ['cabbage', 'lettuce', 'garlic'],
->      ['apple', 'pear', 'banana']]
+> veg = [['lettuce', 'lettuce', 'peppers', 'zucchini'],
+>      ['lettuce', 'lettuce', 'peppers', 'zucchini'],
+>      ['lettuce', 'cilantro', 'peppers', 'zucchini']]
 > ~~~
 > {: .language-python}
 >
-> Here is a visual example of how indexing a list of lists `x` works:
+> Here are some visual examples of how indexing a list of lists `veg` works. First,
+> you can reference each row on the shelf as a separate list. For example, `veg[2]`
+> represents the bottom row, which is a list of the baskets in that row.
 >
-> [![x is represented as a pepper shaker containing several packets of pepper. [x[0]] is represented
-> as a pepper shaker containing a single packet of pepper. x[0] is represented as a single packet of
-> pepper. x[0][0] is represented as single grain of pepper.  Adapted
-> from @hadleywickham.](../fig/indexing_lists_python.png)][hadleywickham-tweet]
+> ![`veg` is now shown as a list of three rows, with `veg[0]` representing the top row of
+> three baskets, `veg[1]` representing the second row, and `veg[2]` representing the bottom row.](../fig/04_groceries_veg0.png)
 >
-> Using the previously declared list `x`, these would be the results of the
-> index operations shown in the image:
+> Index operations using the image would work like this:
 >
 > ~~~
-> print([x[0]])
+> print(veg[2])
 > ~~~
 > {: .language-python}
 >
 > ~~~
-> [['pepper', 'zucchini', 'onion']]
+> ['lettuce', 'cilantro', 'peppers', 'zucchini']
 > ~~~
 > {: .output}
 >
 > ~~~
-> print(x[0])
+> print(veg[0])
+> ~~~
+> {: .language-python}
+>
+> ~~~
+> ['lettuce', 'lettuce', 'peppers', 'zucchini']
+> ~~~
+> {: .output}
+>
+> To reference a specific basket on a specific shelf, you use two indexes. The first
+> index represents the row (from top to bottom) and the second index represents
+> the specific basket (from left to right).
+> ![`veg` is now shown as a two-dimensional grid, with each basket labeled according to
+> its index in the nested list. The first index is the row number and the second
+> index is the basket number, so `veg[1][3]` represents the basket on the far right
+> side of the second row (basket 4 on row 2): zucchini](../fig/04_groceries_veg00.png)
+>
+> ~~~
+> print(veg[0][0])
 > ~~~
 > {: .language-python}
 >
 > ~~~
-> ['pepper', 'zucchini', 'onion']
+> 'lettuce'
 > ~~~
 > {: .output}
 >
 > ~~~
-> print(x[0][0])
+> print(veg[1][2])
 > ~~~
 > {: .language-python}
 >
 > ~~~
-> 'pepper'
+> 'peppers'
 > ~~~
 > {: .output}
 >
-> Thanks to [Hadley Wickham][hadleywickham-tweet]
-> for the image above.
 {: .callout}
 
 > ## Heterogeneous Lists