Recently did many exercises with Python. I have to say it’s really a beautiful language! Lots of cool stuff could be achieved with a single-line function.
Here are some examples. I will add more when I come across them. Please add comments if you think there’s even a better way!
1. Write a function that takes a list, and returns a dictionary with keys the elements of the list and as value the number of occurances of that element in the list:
def count_list(l): return { key: l.count(key) for key in l }
2. Reverse look-up: Write a function that takes a dictionary and a value, and returns the key associated with this value.
def reverse_map(dict, v): return {value: key for key, value in dict.items()}[v]
3. Print the numbers 1 to 100 that are divisible by 5 but not by 3:
Method 1:
x1=range(101)
print filter(lambda x1: x1 % 5 == 0 and x1 % 3 != 0, x1)
Method 2:
[i for i in range(101) if i%5==0 and i%3!=0]
4. Loop over elements and indexes of a list, print them in a given form:
myList=[1, 2, 4]
for index, elem in enumerate(myList): print ‘{0} ) {1}’.format(index, elem)
result:
0) 1
1) 2
2) 4
5. Nearest neighbor – Write a function that takes a value z and an array A and finds the element in A that is closest to z. The function should return the closest value, not index
def find_nearest(a, a0):
return a.flat[np.abs(a – a0).argmin()]
**More to come!
Data Mining, Business Intelligence 