Python:如何按最常见的第一个元素对列表列表进行排序？

Question

如何根据第一个元素的数量对列表列表进行排序？例如，如果下面有以下列表，我希望对列表进行排序，以便所有“佐治亚大学”条目排在第一位，然后是“密歇根大学”条目，然后是“佛罗里达大学”条目。

l = [['University of Michigan','James Jones','phd'],
     ['University of Georgia','Anne   Greene','ba'],
     ['University of Michigan','Frank Kimball','ma'],
     ['University of Florida','Nate Franklin','ms'],
     ['University of Georgia','Sara Dean','ms'],
     ['University of Georgia','Beth Johnson','bs']]

Answer 1

from collections import Counter
c = Counter(item[0] for item in l)
print sorted(l, key = lambda x: -c[x[0]])

输出

[['University of Georgia', 'Anne   Greene', 'ba'],
 ['University of Georgia', 'Sara Dean', 'ms'],
 ['University of Georgia', 'Beth Johnson', 'bs'],
 ['University of Michigan', 'James Jones', 'phd'],
 ['University of Michigan', 'Frank Kimball', 'ma'],
 ['University of Florida', 'Nate Franklin', 'ms']]

普通字典版本:

c = {}
for item in l:
    c[item[0]] = c.get(item[0], 0) + 1
print sorted(l, key = lambda x: -c[x[0]])

defaultdict 版本:

from collections import defaultdict
c = defaultdict(int)
for item in l:
    c[item[0]] += 1
print sorted(l, key = lambda x: -c[x[0]])