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.