numpy学习--运算

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加/减

import numpy as np

a=np.array([10,20,30,40])
b=np.arange(4)
print(a,b)	//[10 20 30 40] [0 1 2 3]
c = a+b
print(c)    //[10 21 32 43]

乘方

c = b**2		
print(c)	//[0 1 4 9]

三角函数

c = 10*np.sin(a)
print(c)	//[-5.44021111  9.12945251 -9.88031624  7.4511316 ]
//还有
//np.cos()	np.tan()

按条件统计

print(b<3)	//[ True  True  True False]
print(b==3)	//[False False False  True]

矩阵运算

a = np.array([[1,1],
			  [0,1]])
b = np.arange(4).reshape((2,2))
print(a)	//[[1 1]
			//[0 1]]
print(b)	//[[0 1]
			//[2 3]]
//点乘
c = a*b		
//矩阵乘
c_dot = np.dot(a,b)
//或 
c_dot2 = a.dot(b)
print(c)		//[[0 1]
				//[0 3]]
print(c_dot)	//[[2 4]
				//[2 3]]

求array和、最小值、最大值

import numpy as np

a = np.random.random((2,4))
np.sum(a)
np.max(a)
np.mim(a)

//求某一行（维度）
np.sum(a,axis=1) 	//每行上求和
np.max(a,axis=0)	//每列上求最大值
np.min(a,axis=1)	//每行上求最小值

其他运算

A = np.arange(2,14).reshape((3,4))
print(A)					//[[ 2  3  4  5]
							// [ 6  7  8  9]
							// [10 11 12 13]]
min_index = np.argmin(A)	//最小值下标
max_index = np.argmax(A)	//最大值小标
mean = np.mean(A)			//平均值
//或
//A.mean()
median = np.median(A)		//中位数

cumsum = np.cumsum(A)		//累加
diff = np.diff(A)			//临差

nonzero = np.nonzero(A)		//非零元素所在的行和列

sort = np.sort(A)			//排序

tran = np.transpose(A)				//矩阵转置
//或
A.T
例如
A.T.dot(A)

clip = np.clip(A,5,9)				//所有小于5的都等于5，所有大于9的都等于9

np.mean(A,axis=0)			//按列进行计算求平均值

print(min_index)			//0
print(max_index)			//11
print(mean)					//7.5
print(median)				//7.5
print(cumsum)				//[ 2  5  9 14 20 27 35 44 54 65 77 90]
print(diff)					//[[1 1 1]
							// [1 1 1]
							// [1 1 1]]
print(nonzero)				//(array([0, 0, 0, 0, 1, 1, 1, 1, 2, 2, 2, 2], dtype=int64), array([0, 1, 2, 3, 0, 1, 2, 3, 0, 1, 2, 3], dtype=int64))



//另一种老版本平均值算法
np.average(A)