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What is 'Pattern Matching' in functional languages?
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Understanding pattern matching requires explaining three parts:
Algebraic data types.
What pattern matching is
Why its awesome.
Algebraic data types in a nutshell
ML-like functional languages allow you define simple data types called "disjoint unions" or "algeb...
How do I check if a list is empty?
For example, if passed the following:
27 Answers
27
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How do I check if there are duplicates in a flat list?
For example, given the list ['one', 'two', 'one'] , the algorithm should return True , whereas given ['one', 'two', 'three'] it should return False .
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Find indices of elements equal to zero in a NumPy array
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numpy.where() is my favorite.
>>> x = numpy.array([1,0,2,0,3,0,4,5,6,7,8])
>>> numpy.where(x == 0)[0]
array([1, 3, 5])
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ASP.NET MVC: Unit testing controllers that use UrlHelper
One of my controllers actions, one that is being called in an Ajax request, is returning an URL to the client side so it can do a redirection. I'm using Url.RouteUrl(..) and during my unit tests this fails since the Controller.Url parameter is not pre-filled.
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What is the 'pythonic' equivalent to the 'fold' function from functional programming?
...ce (from the functools module) and the operator module, e.g.:
def product(xs):
return reduce(operator.mul, xs, 1)
Be aware that reduce is actually a foldl, in Haskell terms. There is no special syntax to perform folds, there's no builtin foldr, and actually using reduce with non-associative o...
How to “properly” print a list?
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In Python 2:
mylist = ['x', 3, 'b']
print '[%s]' % ', '.join(map(str, mylist))
In Python 3 (where print is a builtin function and not a syntax feature anymore):
mylist = ['x', 3, 'b']
print('[%s]' % ', '.join(map(str, mylist)))
Both return:
[x...
How to sort a list of lists by a specific index of the inner list?
I have a list of lists. For example,
10 Answers
10
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How to use timeit module
...care is required so that one pass at an in-place sort doesn't affect the next pass with already sorted data (that, of course, would make the Timsort really shine because it performs best when the data already partially ordered).
Here is an example of how to set up a test for sorting:
>>> ...
Rotating and spacing axis labels in ggplot2
I have a plot where the x-axis is a factor whose labels are long. While probably not an ideal visualization, for now I'd like to simply rotate these labels to be vertical. I've figured this part out with the code below, but as you can see, the labels aren't totally visible.
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