Python-Numpy(1)Array数组

import numpyworld_alcohol = numpy.genfromtxt("world_alcohol.txt", delimiter=",")print(type(world_alcohol))

#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])#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]])print vectorprint matrix

#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)

#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

#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

world_alcohol = numpy.genfromtxt("world_alcohol.txt", delimiter=",", dtype="U75", skip_header=1)print(world_alcohol)

uruguay_other_1986 = world_alcohol[1,4]third_country = world_alcohol[2,2]print uruguay_other_1986print third_country

vector = numpy.array([5, 10, 15, 20])print(vector[0:3])  

matrix = numpy.array([                    [5, 10, 15],                     [20, 25, 30],                    [35, 40, 45]                 ])print(matrix[:,1])

matrix = numpy.array([                    [5, 10, 15],                     [20, 25, 30],                    [35, 40, 45]                 ])print(matrix[:,0:2])

matrix = numpy.array([                    [5, 10, 15],                     [20, 25, 30],                    [35, 40, 45]                 ])print(matrix[1:3,0:2])

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