纯python实现Numpy部分高级运算

更新于
使用纯python实现常用的求极差、平均数、中位数、众数与方差等功能。
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import time
import random

class PON:
    # 求极差
    @staticmethod
    def range(l):
        return max(l) - min(l)
    # 求平均数
    @staticmethod
    def avg(l):
        return float(sum(l))/len(l)
    # 求中位数
    @staticmethod
    def median(l):
        l = sorted(l)
        if len(l)%2 == 1:
            return l[int(len(l)/2)]
        else:
            return (l[int(len(l)/2)-1]+l[int(len(l)/2)]) /2.0
    # 求众数
    @staticmethod
    def mode(l):
        count_dict = {}
        for i in l:
            if i in count_dict:
                count_dict[i] += 1
            else:
                count_dict[i] = 1
        max_appear = 0
        for v in count_dict.values():
            if v > max_appear:
                max_appear = v
        if max_appear == 1:
            return 
        mode_list = []
        for k,v in count_dict.items():
            if v == max_appear:
                mode_list.append(k)
        return mode_list
    # 求方差
    @staticmethod
    def variance(l): # 平方的期望-期望的平方
        s1 = 0
        s2 = 0
        for i in l:
            s1 += i**2
            s2 += i
        return float(s1)/len(l) - (float(s2)/len(l))**2
    # 求方差2
    @staticmethod    
    def variance2(l): # 平方-期望的平方的期望
        ex = float(sum(l))/len(l)
        s = 0
        for i in l:
            s += (i-ex)**2
        return float(s)/len(l)    
 
# 主函数，测试
arr = [1,2,3,2,3,1,4]
print("极差为：{0}".format(PON.range(arr)))
print("平均数为：{0:.2f}".format(PON.avg(arr)))
print("中位数为：{0}".format(PON.median(arr)))
print("众数为：{0}".format(PON.mode(arr)))
print("方差为：{0:.2f}".format(PON.variance(arr)))
print("方差为：{0:.2f}".format(PON.variance2(arr)))

 
# 性能测试
arraylist = []
for i in range(1,1000000):
    arraylist.append(i)
random.shuffle(arraylist)
time_start = time.time()
print("方差为：{0:.2f}".format(PON.variance(arraylist)))
time_end = time.time()
print("{0}s".format(time_end-time_start))
time_start = time.time()
print("方差为：{0:.2f}".format(PON.variance2(arraylist)))
time_end = time.time()
print("{0}s".format(time_end-time_start))
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