python数据分析之NumPy数据存取与函数3

NumPy中的统计函数

sum(a,axis = None)：根据给定轴axis计算数组a相关元素之和，axis整数或元组
mean(a,axis = None)：根据给定轴axis计算数组a相关元素的期望，axis整数或元组
average(a,axis = None,weights = None)：根据给定轴axis计算数组a相关元素的加权平均值
std(a,axis = None)：根据给定轴axis计算数组a相关元素的标准差
var(a,axis = None)：根据给定轴axis计算数组a相关元素的方差

np.min(a,axis = None)或a.min(axis = None),np.max(a,axis = None)或a.max(axis = None)：计算数组a中元素的最小值、最大值

import numpy as np
a = np.array([[1,5,3],[4,2,6]])
print(a.min()) #无参，所有中的最小值
print(a.min(0)) # axis=0; 每列的最小值
print(a.min(1)) # axis=1；每行的最小值

np.argmin(a,axis = None)或a.argmin(axis = None),np.argmax(a,axis = None)或a.argmax(axis = None)：计算数组a中元素的最小值、最大值的降一维后下标
unravel_index(index,shape)：根据shape将一维下标index转换成多维下标

a = np.arange(15).reshape(3,5)
np.random.shuffle(a)
print(a)
np.argmin(a)
index = np.unravel_index(np.argmin(a),a.shape)
print(index)

ptp(a)：计算数组a中元素最大值与最小值的差
median(a)：计算数组a中元素的中位数