为什么提取函数给出错误的数组

Question

我有一个二维数组，我想只返回一个新数组中的男学生。我想专门使用提取功能。但是，条件是正确的，但是提取函数给出了错误的输出。

# creating an a numpy array with the names of students along with their corresponding biological sex
students=np.array([["alexis", "female"],["alex", "male"], ["david", "non-binary"], ["samar", "male"], ["anweshan","male"]])

# creating a condition to check if a student is a male or not

con = students[0: , 1] == "male"

#creating a new array with only the male students
male_students = np.extract(con, students)
print(male_students)

这给出了错误的输出，如下所示

['女''男''大卫']

但是，以不同的方式编写代码会产生正确的输出。代码如下：

# creating an a numpy array with the names of students along with their corresponding biological sex
students=np.array([["alexis", "female"],["alex", "male"], ["david", "non-binary"], ["samar", "male"], ["anweshan","male"]])

# creating a condition to check if a student is a male or not

con1 = students[0: , 1] == "male"
print(con1)
print(students[con1])

它给出以下输出

[['alex''男'] ['萨马尔''男性'] ['anweshan' '男']]

我想使用提取功能，请问我哪里出错了？

Answer 1

你的 con 数组的形状不一样。

con = students[: , 1] == "male"

con_same_shape = np.empty((5,2))

con_same_shape[:,0] = con
con_same_shape[:,1] = con

#creating a new array with only the male students
male_students = np.extract(con_same_shape, students)

print(male_students)

将返回：

['alex' 'male' 'samar' 'male' 'anweshan' 'male']