python-按行更新数据帧但不更新

我正在遍历数据框,并尝试将值添加到每一行的特定列中,但是当我打印结果数据框时,值不存在

#add two new blank columns to the dayData dataframe 
dayData["myValue1"]=""
dayData["myValue2"]=""

#iterate over the dataframe
for idxDay, row in dayData.iterrows():
        do something.....
        #interate again through the dataframe
        for idxrange, row1 in dayData.iterrows():
            do something else....
            calculate value1
            calculate value2 

        #write the result for value1 and value2 to the dayData dataframe         


        row["myValue1"]=value1
        row["myValue2"]=value2
        print(dayData)

value1和value 2的值是正确的,即使当我硬编码value1 = 1和value2 = 2时(当我打印dayData时,应更新myValue1和myValue2列之后的列,它们也不包含任何数据).

最终的dayData数据框应该看起来像

         vwap        last       volume     ratio myLong myShort  
0  301.071871  301.221525   43133218.0  1.000497   1       2       
1  215.545413  213.791400  349730738.0  0.991862   3       3

但是我得到的只是：

         vwap        last       volume     ratio myLong myShort  
0  301.071871  301.221525   43133218.0  1.000497                 
1  215.545413  213.791400  349730738.0  0.991862          

解决方法:

代替分配给行,而是分配给带有索引的数据框.该行是该行的副本,对其所做的更改将不会保留在父数据框中.

代替：

        row["myValue1"]=value1
        row["myValue2"]=value2

做：

        dayData.loc[idxDay, "myValue1"]=value1
        dayData.loc[idxDay, "myValue2"]=value2

进一步的例子：

df = pd.DataFrame([1], ['a'], ['A'])

print df

   A
a  1

for i, r in df.iterrows():
    r.loc['B'] = 2

print df

   A
a  1


for i, r in df.iterrows():
    df.loc[i, 'B'] = 2

print df

   A    B
a  1  2.0

清楚地表明分配给行不起作用.分配给数据框.