Numpy具体用法相关内容（一）
#!/usr/bin/env python# coding: utf-8# ## 1、使用numpy读取txt文件数据# # In[3]:import numpyworld_alcohol = numpy.genfromtxt("world_alcohol.txt", delimiter=",") # 使用numpy加载txt文件print(type(world_alcohol))print(world_alcohol)# ## 2、使用numpy定义数组# In[4]:#The numpy.array() function can take a list or list of lists as input. When we input a list, we get a one-dimensional array as a result:vector = numpy.array([5, 10, 15, 20]) # 生成一维的数组数据#When we input a list of lists, we get a matrix as a result:matrix = numpy.array([[5, 10, 15], [20, 25, 30], [35, 40, 45]]) # 生成二维的数组数据print(vector)print(matrix)# ## 3、打印数组的维度# In[5]:#We can use the ndarray.shape property to figure out how many elements are in the arrayvector = numpy.array([1, 2, 3, 4])print(vector.shape)#For matrices, the shape property contains a tuple with 2 elements.matrix = numpy.array([[5, 10, 15], [20, 25, 30]])print(matrix.shape)# ## 4、获取数组的类型# In[6]:#Each value in a NumPy array has to have the same data type#NumPy will automatically figure out an appropriate data type when reading in data or converting lists to arrays. #You can check the data type of a NumPy array using the dtype property.numbers = numpy.array([1, 2, 3, 4])numbers.dtype# In[7]:#When NumPy can't convert a value to a numeric data type like float or integer, it uses a special nan value that stands for Not a Number#nan is the missing data#1.98600000e+03 is actually 1.986 * 10 ^ 3world_alcohol# In[8]:world_alcohol = numpy.genfromtxt("world_alcohol.txt", delimiter=",", dtype="U75", skip_header=1) # skip_header=1:表示跳过第一行的标题栏print(world_alcohol)# ## 5、获取数组中的元素# In[11]:uruguay_other_1986 = world_alcohol[1,4]third_country = world_alcohol[2,2]print(uruguay_other_1986)print(third_country)# In[13]:vector = numpy.array([5, 10, 15, 20])print(vector[0:3]) # 包头不包尾# In[16]:matrix = numpy.array([ [5, 10, 15],[20, 25, 30], [35, 40, 45] ])# 获取二维数组中某列元素print(matrix[:,1])# In[17]:matrix = numpy.array([ [5, 10, 15],[20, 25, 30], [35, 40, 45] ])# # 获取二维数组中某几列元素print(matrix[:,0:2])# In[18]:matrix = numpy.array([ [5, 10, 15],[20, 25, 30], [35, 40, 45] ])print(matrix[1:3,0:2])
推币机的世界
