计算某种类型的词典数量

Question

I have a list of dictionaries. Each dictionary has a colour attribute. For example:

{'att1':value1, 'att2': value2, 'colour': 'Red'}

The colou attribute is from a list of 15 maxium colours.

I have over a thousand of these dictionaries in the list. I need to find out what is the popular colour and how many instances of it there are? Simiilarly I need the second most popular colour, the number of instances of it, the third most, fourth most etc...

Can some fancy pythonic syntax help me out?

Answer 1

from collections import defaultdict
colours = defaultdict(int)
for item in mylist:
   colours[item["colour"]] +=1

gives you a defaultdict with all the colours and their respective number. Displaying those in a sorted fashion is trivial.

Answer 2

You could use Counter and generator like this:

distribution = collections.Counter(d['colour'] for d in list_of_dict)
distribution.most_common(2)

Answer 3

Use map to map each dictionary to its colors, then a collections.Counter . Should be a one-liner this way. Something like

collections.Counter(map(lambda x: x.get("color"), listofdict))

Answer 4

l = []
for x in xrange(100):
   l.append({'att1':1, 'att2': 2, 'colour': 'Red'})

for x in xrange(10):
   l.append({'att1':1, 'att2': 2, 'colour': 'Blue'})

colors = [i['colour'] for i in l]

dcolors = {}
for i in colors:
   if not i in dcolors:
       dcolors[i] = 0
   dcolors[i] += 1

print dcolors

I created 100 red and 10 blue items, the print result is:

{'Blue': 10, 'Red': 100}

You probably can find a way to find the max etc or sort it.