求某列数据的平均数（mean）
此处需要用到numpy
求test列的平均数： numpy.mean(test)
求test列的标准差： numpy.sdt(test)
求test列的中位数 : numpy.median(test)
下面有一题：求金牌数不小于1的所以国家的银牌数的平均数：
数据：
countries = ['Russian Fed.', 'Norway', 'Canada', 'United States',
'Netherlands', 'Germany', 'Switzerland', 'Belarus',
'Austria', 'France', 'Poland', 'China', 'Korea',
'Sweden', 'Czech Republic', 'Slovenia', 'Japan',
'Finland', 'Great Britain', 'Ukraine', 'Slovakia',
'Italy', 'Latvia', 'Australia', 'Croatia', 'Kazakhstan']
gold = [13, 11, 10, 9, 8, 8, 6, 5, 4, 4, 4, 3, 3, 2, 2, 2, 1, 1, 1, 1, 1, 0, 0, 0, 0, 0]
silver = [11, 5, 10, 7, 7, 6, 3, 0, 8, 4, 1, 4, 3, 7, 4, 2, 4, 3, 1, 0, 0, 2, 2, 2, 1, 0]
bronze = [9, 10, 5, 12, 9, 5, 2, 1, 5, 7, 1, 2, 2, 6, 2, 4, 3, 1, 2, 1, 0, 6, 2, 1, 0, 1]
olympic_medal_counts = {'country_name':Series(countries),
'gold': Series(gold),
'silver': Series(silver),
'bronze': Series(bronze)}
df = DataFrame(olympic_medal_counts)
看下数据框显示：
bronze country_name gold silver
0 9 Russian Fed. 13 11
1 10 Norway 11 5
2 5 Canada 10 10
3 12 United States 9 7
4 9 Netherlands 8 7
5 5 Germany 8 6
6 2 Switzerland 6 3
7 1 Belarus 5 0
8 5 Austria 4 8
9 7 France 4 4
10 1 Poland 4 1
11 2 China 3 4
12 2 Korea 3 3
13 6 Sweden 2 7
14 2 Czech Republic 2 4
15 4 Slovenia 2 2
16 3 Japan 1 4
17 1 Finland 1 3
18 2 Great Britain 1 1
19 1 Ukraine 1 0
20 0 Slovakia 1 0
21 6 Italy 0 2
22 2 Latvia 0 2
23 1 Australia 0 2
24 0 Croatia 0 1
25 1 Kazakhstan 0 0
- 结题思路：
1). 获取所有金牌数大于0的国家的数据
at_least_one_gold = df[df.gold > 0]
输出结果：
bronze country_name gold silver
0 9 Russian Fed. 13 11
1 10 Norway 11 5
2 5 Canada 10 10
3 12 United States 9 7
4 9 Netherlands 8 7
5 5 Germany 8 6
6 2 Switzerland 6 3
7 1 Belarus 5 0
8 5 Austria 4 8
9 7 France 4 4
10 1 Poland 4 1
11 2 China 3 4
12 2 Korea 3 3
13 6 Sweden 2 7
14 2 Czech Republic 2 4
15 4 Slovenia 2 2
16 3 Japan 1 4
17 1 Finland 1 3
18 2 Great Britain 1 1
19 1 Ukraine 1 0
20 0 Slovakia 1 0
2). 只筛选出银牌数据：
bronze_at_least_one_gold = at_least_one_gold['bronze']
数据：
0 9
1 10
2 5
3 12
4 9
5 5
6 2
7 1
8 5
9 7
10 1
11 2
12 2
13 6
14 2
15 4
16 3
17 1
18 2
19 1
20 0
3). 求出平均数：
avg_bronze_at_least_one_gold = numpy.mean(bronze_at_least_one_gold)
结果： 4.2380952381
