【numpy】20道numpy题目

2023-08-05 04:28| 来源: 网络整理| 查看: 265

1、创建一个长度为10的一维全为0的ndarray对象，然后让第5个元素等于1

import numpy as np ndarry =np.zeros(10) ndarry array([0., 0., 0., 0., 0., 0., 0., 0., 0., 0.]) ndarry[4]=1 ndarry array([0., 0., 0., 0., 1., 0., 0., 0., 0., 0.])

2、创建一个元素为从10到49的ndarray对象

ndarray = np.arange(10,50) ndarray array([10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49])

3、将第2题的所有元素位置反转

ndarray[::-1] array([49, 48, 47, 46, 45, 44, 43, 42, 41, 40, 39, 38, 37, 36, 35, 34, 33, 32, 31, 30, 29, 28, 27, 26, 25, 24, 23, 22, 21, 20, 19, 18, 17, 16, 15, 14, 13, 12, 11, 10])

使用np.random.random创建一个10*10的ndarray对象，并打印出最大最小元素

ndarray = np.random.random((10,10)) ndarray ndarray.min() 0.009073749212965887

5、创建一个10*10的ndarray对象，且矩阵边界全为1，里面全为0

a=np.zeros((10,10),dtype=np.int8) a[[0,-1]]=1 a[:,[0,-1]]=1 a array([[1, 1, 1, 1, 1, 1, 1, 1, 1, 1], [1, 0, 0, 0, 0, 0, 0, 0, 0, 1], [1, 0, 0, 0, 0, 0, 0, 0, 0, 1], [1, 0, 0, 0, 0, 0, 0, 0, 0, 1], [1, 0, 0, 0, 0, 0, 0, 0, 0, 1], [1, 0, 0, 0, 0, 0, 0, 0, 0, 1], [1, 0, 0, 0, 0, 0, 0, 0, 0, 1], [1, 0, 0, 0, 0, 0, 0, 0, 0, 1], [1, 0, 0, 0, 0, 0, 0, 0, 0, 1], [1, 1, 1, 1, 1, 1, 1, 1, 1, 1]], dtype=int8)

6、创建一个每一行都是从0到4的5*5矩阵

a=np.array([0,1,2,3,4]*5).reshape(5,5) a array([[0, 1, 2, 3, 4], [0, 1, 2, 3, 4], [0, 1, 2, 3, 4], [0, 1, 2, 3, 4], [0, 1, 2, 3, 4]])

7、创建一个范围在(0,1)之间的长度为12的等差数列

a=np.linspace(0,1,12) a array([0. , 0.09090909, 0.18181818, 0.27272727, 0.36363636, 0.45454545, 0.54545455, 0.63636364, 0.72727273, 0.81818182, 0.90909091, 1. ])

8、创建一个长度为10的随机数组并排序

a = np.random.randint(1,10,size=10) a.sort() a array([1, 2, 2, 3, 4, 4, 6, 7, 8, 9])

9、创建一个长度为10的随机数组并将最大值替换为0

a = np.random.randint(1,10,10) b=a.max() c=a==b a[c]=0 a,b,c (array([3, 5, 0, 7, 1, 2, 7, 0, 5, 7]),9, array([False, False, True, False, False, False, False, True, False, False]))

10、如何根据第3列来对一个5*5矩阵排序？???

a=np.random.randint(0,25,size=25).reshape(5,5) a array([[ 4, 20, 17, 6, 5], [ 8, 14, 14, 10, 3], [ 7, 5, 12, 7, 4], [15, 1, 7, 5, 24], [12, 14, 16, 12, 2]]) b=np.argsort(a[:,2]) a[b] array([[15, 1, 7, 5, 24], [ 7, 5, 12, 7, 4], [ 8, 14, 14, 10, 3], [12, 14, 16, 12, 2], [ 4, 20, 17, 6, 5]])

11、给定一个4维矩阵，如何得到最后两维的和？

a=np.random.randint(0,10,size=(3,4,5,6)) a.sum(axis=-1).sum(axis=-1) a array([[[[4, 0, 0, 8, 6, 9], [4, 0, 8, 4, 4, 5], [3, 7, 2, 4, 2, 7], [9, 8, 9, 2, 3, 1], [8, 1, 4, 2, 5, 9]], [[7, 5, 5, 7, 6, 2], [3, 5, 3, 4, 7, 1], [0, 5, 7, 7, 6, 7], [5, 8, 7, 9, 8, 3], [6, 9, 2, 6, 0, 5]], [[9, 2, 7, 9, 0, 7], [1, 4, 7, 5, 4, 3], [6, 8, 0, 2, 8, 4], [8, 4, 8, 7, 4, 3], [0, 9, 2, 2, 6, 7]], [[3, 0, 0, 9, 5, 3], [7, 4, 9, 4, 9, 8], [7, 1, 3, 3, 4, 5], [1, 0, 7, 3, 8, 3], [7, 1, 6, 3, 9, 4]]], [[[0, 4, 8, 9, 7, 6], [0, 0, 7, 0, 8, 3], [3, 7, 7, 4, 7, 8], [5, 1, 7, 5, 3, 7], [8, 9, 0, 4, 2, 6]], [[1, 9, 1, 2, 7, 6], [6, 4, 4, 3, 9, 5], [4, 1, 5, 8, 9, 5], [0, 0, 2, 8, 9, 5], [6, 3, 0, 8, 0, 9]], [[5, 4, 9, 2, 9, 8], [2, 7, 4, 3, 5, 8], [8, 8, 0, 4, 4, 8], [7, 5, 1, 6, 1, 1], [1, 8, 1, 0, 4, 4]], [[7, 6, 6, 4, 8, 2], [2, 1, 1, 1, 0, 7], [5, 1, 6, 2, 3, 5], [2, 4, 6, 0, 8, 9], [3, 6, 5, 3, 1, 6]]], [[[1, 8, 1, 7, 2, 5], [3, 0, 9, 3, 8, 0], [5, 2, 1, 0, 8, 4], [4, 1, 3, 8, 4, 3], [4, 8, 8, 2, 6, 2]], [[7, 6, 2, 5, 9, 7], [2, 9, 1, 2, 5, 9], [3, 0, 2, 5, 5, 0], [6, 0, 1, 8, 4, 3], [5, 4, 5, 6, 2, 1]], [[9, 5, 0, 5, 0, 7], [0, 4, 8, 4, 4, 8], [6, 2, 3, 9, 3, 7], [7, 7, 1, 8, 3, 5], [0, 4, 7, 6, 9, 7]], [[2, 1, 4, 6, 7, 8], [8, 6, 0, 5, 8, 1], [9, 4, 8, 2, 8, 5], [0, 6, 2, 3, 9, 6], [8, 7, 4, 2, 7, 6]]]])

12、给定数组[1, 2, 3, 4, 5]，如何得到在这个数组的每个元素之间插入3个0后的新数组？

a=np.arange(1,6) b=np.zeros(17,dtype=np.int8) b[::4]=a b array([1, 0, 0, 0, 2, 0, 0, 0, 3, 0, 0, 0, 4, 0, 0, 0, 5], dtype=int8)

13、给定一个二维矩阵，如何交换其中两行的元素？

a=np.arange(0,20).reshape(4,5) a a[[1,0,2,3]] a array([[ 0, 1, 2, 3, 4], [ 5, 6, 7, 8, 9], [10, 11, 12, 13, 14], [15, 16, 17, 18, 19]])

14、创建一个100000长度的随机数组，使用两种方法对其求三次方，并比较所用时间

import time a=np.random.randn(1000000) a t1 = time.time() np.power(a,3) time= time.time()-t1 time 0.0468747615814209

15、创建一个53随机矩阵和一个32随机矩阵，求矩阵积

a=np.random.randint(0,10,(5,3)) b=np.random.randint(0,10,(3,2)) a,b np.matmul(a,b) array([[ 48, 50], [171, 101], [124, 62], [105, 63], [ 75, 67]])

16、矩阵的每一行的元素都减去该行的平均值

a=np.random.randint(0,10,(3,3)) a b=a.mean(axis=1).reshape(3,1) a-b array([[ 2.66666667, -1.33333333, -1.33333333], [-3. , 3. , 0. ], [-1.33333333, 0.66666667, 0.66666667]])

17、打印出以下函数（要求使用np.zeros创建8*8的矩阵）： [[0 1 0 1 0 1 0 1] [1 0 1 0 1 0 1 0] [0 1 0 1 0 1 0 1] [1 0 1 0 1 0 1 0] [0 1 0 1 0 1 0 1] [1 0 1 0 1 0 1 0] [0 1 0 1 0 1 0 1] [1 0 1 0 1 0 1 0]]

a=np.zeros((8,8),dtype='int') a[::2,1::2]=1 a[1::2,::2]=1 a array([[0, 1, 0, 1, 0, 1, 0, 1], [1, 0, 1, 0, 1, 0, 1, 0], [0, 1, 0, 1, 0, 1, 0, 1], [1, 0, 1, 0, 1, 0, 1, 0], [0, 1, 0, 1, 0, 1, 0, 1], [1, 0, 1, 0, 1, 0, 1, 0], [0, 1, 0, 1, 0, 1, 0, 1], [1, 0, 1, 0, 1, 0, 1, 0]])

18、正则化一个5*5随机矩阵正则的概念：假设a是矩阵中的一个元素，max/min分别是矩阵元素的最大最小值，则正则化后a = (a - min)/(max - min)

a=np.random.randint(0,10,size=(5,5)) amin=a.min() amax=a.max() (a-amin)/(amax-amin) array([[0.44444444, 0.11111111, 0.11111111, 0.33333333, 0.88888889], [0. , 0.88888889, 0.77777778, 1. , 0.11111111], [0.33333333, 0.55555556, 0.66666667, 0.33333333, 0.11111111], [0.55555556, 0.33333333, 1. , 0.77777778, 0.33333333], [0.11111111, 0.33333333, 0.11111111, 0.88888889, 0.77777778]])

19、将一个一维数组转化为二进制表示矩阵。例如 [1,2,3] 转化为 [[0,0,1], [0,1,0], [0,1,1]]

num = 4 n1 = np.arange(num) n1 n2 = np.zeros(shape=(num,num),dtype='int') n2 array([[0, 0, 0, 0], [0, 0, 0, 0], [0, 0, 0, 0], [0, 0, 0, 0]]) for i in range(num): n = n1[i] for j in range(num-1,-1,-1): n2[i][j] = n%2 n = n//2 n2[1::] array([[0, 0, 0, 1], [0, 0, 1, 0], [0, 0, 1, 1]])

20、实现冒泡排序法

arr = np.random.randint(1,10,size=10) for i in range(1, len(arr)): for j in range(0, len(arr)-i): if arr[j] > arr[j+1]: arr[j], arr[j + 1] = arr[j + 1], arr[j] arr array([2, 2, 3, 5, 5, 6, 7, 8, 9, 9])

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