Merge pull request #211 from metavee/gh-pages

Added challenge to 01-numpy.md regarding slicing a vector vs an array
swcarpentry · Jun 21, 2016 · 988b2ba · 988b2ba
2 parents 17e7330 + f673550
commit 988b2ba
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diff --git a/01-numpy.md b/01-numpy.md
@@ -737,3 +737,44 @@ the graphs will actually be squeezed together more closely.)
 > ## Moving plots around {.challenge}
 >
 > Modify the program to display the three plots on top of one another instead of side by side.
+
+> ## Stacking arrays {.challenge}
+>
+> Arrays can be concatenated and stacked on top of one another,
+> using NumPy's `vstack` and `hstack` functions for vertical and horizontal stacking, respectively.
+> 
+> ~~~ {.python}
+> import numpy
+> 
+> A = numpy.array([[1,2,3], [4,5,6], [7, 8, 9]])
+> print('A = ')
+> print(A)
+> 
+> B = numpy.hstack([A, A])
+> print('B = ')
+> print(B)
+> 
+> C = numpy.vstack([A, A])
+> print('C = ')
+> print(C)
+> ~~~
+> 
+> ~~~ {.output}
+> A = 
+> [[1 2 3]
+>  [4 5 6]
+>  [7 8 9]]
+> B = 
+> [[1 2 3 1 2 3]
+>  [4 5 6 4 5 6]
+>  [7 8 9 7 8 9]]
+> C = 
+> [[1 2 3]
+>  [4 5 6]
+>  [7 8 9]
+>  [1 2 3]
+>  [4 5 6]
+>  [7 8 9]]
+> ~~~
+> 
+> Write some additional code that slices the first and last columns of `A`, and stacks them into a 3x2 array. Make sure to `print` the results to verify your solution.