Say I have a list of countries
l = ['India', 'China', 'China', 'Japan', 'USA', 'India', 'USA']
and then I have a list of unique countries
ul = ['India', 'China', 'Japan', 'USA']
I want to have a count of each unique country in the list in ascending order. So output should be as follows:
Japan 1
China 2
India 2
USA 2
You can use Counter from collections:
from collections import Counter
l = ["India", "China", "China", "Japan", "USA", "India", "USA"]
new_vals = Counter(l).most_common()
new_vals = new_vals[::-1] #this sorts the list in ascending order
for a, b in new_vals:
print a, b
Counter(l).items() guaranteed to return a a list sorted by count? I think you need to use most_common()
Counter docs give this recipe for n least common: c.most_common()[:-n-1:-1] - which simplifies to the usual [::-1] if n is equal to the total number of items.
If you don't want to use a Counter you can count yourself (you already know the unique elements because you have ul) using a dictionary:
l = ['India', 'China', 'China', 'Japan', 'USA', 'India', 'USA']
ul = ['India', 'China', 'Japan', 'USA']
cnts = dict.fromkeys(ul, 0) # initialize with 0
# count them
for item in l:
cnts[item] += 1
# print them in ascending order
for name, cnt in sorted(cnts.items(), key=lambda x: x[1]): # sort by the count in ascending order
print(name, cnt)
# or in case you need the correct formatting (right padding for the name):
# print('{:<5}'.format(name), cnt)
which prints:
Japan 1
China 2
India 2
USA 2
If you want to sort depending on the ul list, you can use list comprehension like:
l = ['India', 'China', 'China', 'Japan', 'USA', 'India', 'USA']
ul = ['India', 'China', 'Japan', 'USA']
result = sorted([(x, l.count(x)) for x in ul], key=lambda y: y[1])
for elem in result:
print '{} {}'.format(elem[0], elem[1])
output:
Japan 1
India 2
China 2
USA 2
And if you want to sort by alphabet after sorting by count, you can change result to the following:
result = sorted(sorted([(x, l.count(x)) for x in ul]), key=lambda y: y[1])
output:
Japan 1
China 2
India 2
USA 2
count is significantly slower than the Counter approach - order n^2 compared to order n just to count. See this answer for profiling: stackoverflow.com/a/23909767/2337736
ul_set = frozenset(ul); counts = Counter(country for country in countries if country in ul_set) - you really want to avoid running count multiple times on the same list. I mean, it's fine for short lists, but you might as well use the faster tools.