import time 
start = time.time()

# 遍历之和
total = 0
# 遍历150万个数字
for item in range(0, 1500000):
    total = total + item

print('sum is:' + str(total))
end = time.time()

print(end - start)

#1124999250000
#0.14 Seconds
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import numpy as np

start = time.time()

# 向量化和--使用numpy进行向量化
# np.range创建从0到1499999的数字序列
print(np.sum(np.arange(1500000)))

end = time.time()
print(end - start)

##1124999250000
##0.008 Seconds
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import numpy as np
import pandas as pd
df = pd.DataFrame(np.random.randint(0, 50, 
                                    size=(5000000, 4)),
                  columns=('a','b','c','d'))
df.shape
# (5000000, 5)
df.head()
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import time 
start = time.time()

# Iterating through DataFrame using iterrows
for idx, row in df.iterrows():
    # creating a new column 
    df.at[idx,'ratio'] = 100 * (row["d"] / row["c"])  
end = time.time()
print(end - start)
### 109 Seconds
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start = time.time()
df["ratio"] = 100 * (df["d"] / df["c"])

end = time.time()
print(end - start)
### 0.12 seconds
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import time 
start = time.time()

# Iterating through DataFrame using iterrows
for idx, row in df.iterrows():
    if row.a == 0:
        df.at[idx,'e'] = row.d    
    elif (row.a <= 25) & (row.a > 0):
        df.at[idx,'e'] = (row.b)-(row.c)    
    else:
        df.at[idx,'e'] = row.b + row.c

end = time.time()

print(end - start)
### Time taken: 177 seconds
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start = time.time()
df['e'] = df['b'] + df['c']
df.loc[df['a'] <= 25, 'e'] = df['b'] -df['c']
df.loc[df['a']==0, 'e'] = df['d']end = time.time()
print(end - start)
## 0.28007707595825195 sec
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>>> import numpy as np
>>> # 设置 m 的初始值 
>>> m = np.random.rand(1,5)
array([[0.49976103, 0.33991827, 0.60596021, 0.78518515, 0.5540753]])
>>> # 500万行的输入值
>>> x = np.random.rand(5000000,5)
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import numpy as np
m = np.random.rand(1,5)
x = np.random.rand(5000000,5)

total = 0
tic = time.process_time()

for i in range(0,5000000):
    total = 0
    for j in range(0,5):
        total = total + x[i][j]*m[0][j] 
        
    zer[i] = total 

toc = time.process_time()
print ("Computation time = " + str((toc - tic)) + "seconds")

####Computation time = 28.228 seconds
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tic = time.process_time()

#dot product 
np.dot(x,m.T) 

toc = time.process_time()
print ("Computation time = " + str((toc - tic)) + "seconds")

####Computation time = 0.107 seconds
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