我试图弄清楚如何使用多个条件来计算DataFrame中的出现次数。在此特定示例中，我想知道Pclass 3中的女性乘客人数。
PassengerId Pclass Sex Age SibSp Parch Ticket Fare Cabin Embarked
0 892 3 male 34.5 0 0 330911 7.8292 NaN Q
1 893 3 female 47.0 1 0 363272 7.0000 NaN S
2 894 2 male 62.0 0 0 240276 9.6875 NaN Q
3 895 3 male 27.0 0 0 315154 8.6625 NaN S
4 896 3 female 22.0 1 1 3101298 12.2875 NaN S
这是我的几次失败尝试：
len(test[test["Sex"] == "female", test["Pclass"] == 3])
sum(test.Pclass == 3 & test.Sex == "female")
test.[test["Sex"] == "female", test["Pclass"] == 3].count()
他们似乎都没有工作。最后，我创建了自己的函数，但是必须有一种更简单的方法来计算该函数。
def countif(sex, pclass):
x = 0
for i in range(0,len(test)):
s = test.iloc[i]['Sex']
c = test.iloc[i]['Pclass']
if s == sex and c == pclass:
x = x + 1
return x
先感谢您
有几种方法可以做到这一点：
test = pd.DataFrame({'PassengerId': {0: 892, 1: 893, 2: 894, 3: 895, 4: 896},
'Pclass': {0: 3, 1: 3, 2: 2, 3: 3, 4: 3},
'Sex': {0: 'male', 1: 'female', 2: 'male', 3: 'male', 4: 'female'},
'Age': {0: 34.5, 1: 47.0, 2: 62.0, 3: 27.0, 4: 22.0},
'SibSp': {0: 0, 1: 1, 2: 0, 3: 0, 4: 1},
'Parch': {0: 0, 1: 0, 2: 0, 3: 0, 4: 1},
'Ticket': {0: 330911, 1: 363272, 2: 240276, 3: 315154, 4: 3101298},
'Fare': {0: 7.8292, 1: 7.0, 2: 9.6875, 3: 8.6625, 4: 12.2875},
'Cabin': {0: np.nan, 1: np.nan, 2: np.nan, 3: np.nan, 4: np.nan},
'Embarked': {0: 'Q', 1: 'S', 2: 'Q', 3: 'S', 4: 'S'}})
您需要将布尔值放在圆括号中，并与＆
sum((test.Pclass == 3) & (test.Sex == "female"))
len(test[(test.Pclass == 3) & (test.Sex == "female")])
test[(test["Sex"] == "female") & (test["Pclass"] == 3)].shape[0]
或者您可以执行以下操作：
tab = pd.crosstab(df.Pclass,df.Sex)
Sex female male
Pclass
2 0 1
3 2 2
tab.iloc[tab.index==3]['female']
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