numpy的100个练习解析(持续更新)

numpy100个练习解析

先放链接https://github.com/rougier/numpy-100/blob/master/100_Numpy_exercises.md

1. Import the numpy package under the name np (★☆☆)

import numpy as np

可以下载Anaconda，里面带有很多python库。

以下默认已经引入numpy库

2. Print the numpy version and the configuration (★☆☆)

print(np.__version__)
np.show_config()

3. Create a null vector of size 10 (★☆☆)

A=np.zeros(10)
print(A)

创建一个大小为10的零向量

4. How to find the memory size of any array (★☆☆)

A=np.zeros(10)
print(A.size * A.itemsize,"bytes")

size元素个数，itemsize每个元素的大小

5. How to get the documentation of the numpy add function from the command line? (★☆☆)

np.info(np.add)

x1 = np.arange(9.0).reshape((3, 3))
x2 = np.arange(3.0)
print(np.add(x1, x2))
'''
值得注意的是，若两个矩阵维度不相同也可以利用add相加，结果如下所示：
[[ 0.  2.  4.]
 [ 3.  5.  7.]
 [ 6.  8. 10.]]
'''

6. Create a null vector of size 10 but the fifth value which is 1 (★☆☆)

A=np.zeros(10)
A[4]=1

注意第五个元素应该是A[4]

7. Create a vector with values ranging from 10 to 49 (★☆☆)

A=np.arange(10,50)

arange(start,end)表示从start到end-1

8. Reverse a vector (first element becomes last) (★☆☆)

A=np.arange(0,5)
A=A[::-1]

9. Create a 3x3 matrix with values ranging from 0 to 8 (★☆☆)

A= np.arange(9).reshape(3,3)

10. Find indices of non-zero elements from [1,2,0,0,4,0] (★☆☆)

index=np.nonzero([1,2,0,0,4,0])
print(index)

11. Create a 3x3 identity matrix (★☆☆)

A=np.eye(3)

12. Create a 3x3x3 array with random values (★☆☆)

A=np.random.random((3,3,3))

13. Create a 10x10 array with random values and find the minimum and maximum values (★☆☆)

A = np.random.random((10, 10))
B = A.max()
C = A.min()

14. Create a random vector of size 30 and find the mean value (★☆☆)

A = np.random.random(30)
print(A.mean())

15. Create a 2d array with 1 on the border and 0 inside (★☆☆)

A=np.ones((5,5))
A[1:-1,1:-1]=0
print(A)