Python熊猫通过遍历列来构建数据框

Question

I am trying to develop a new panda dataframe based on data I got from an existing dataframe and then taking into account the previously calculated value in the new dataframe.

As an example, here are two dataframes with the same size.

df1 = pd.DataFrame(np.random.randint(0,10, size = (5, 4)), columns=['1', '2', '3', '4'])
df2 = pd.DataFrame(np.zeros(df1.shape), index=df1.index, columns=df1.columns)

Then I created a list which starts as a starting basis for my second dataframe df2

L = [2,5,6,7]

df2.loc[0] = L

Then for the remaining rows of df2 I want to take the value from the previous time step (df2) and add the value of df1.

for i in df2.loc[1:]:
   df2.ix[i] = df2.ix[i-1] + df1

As an example my dataframes should look like this:

>>> df1
   1  2  3  4
0  4  6  0  6
1  7  0  7  9
2  9  1  9  9
3  5  2  3  6
4  0  3  2  9
>>> df2
   1  2  3  4
0  2  5  6  7
1  9  5  13 16
2  18 6  22 25
3  23 8  25 31
4  23 11 27 40

I know there is something wrong with the indication of indexes in the for loop but I cannot figure out how the argument must be formulated. I would be very thankful for any help on this.

Answer 1

this is a simple cumsum .

df2 = df1.copy()
df2.loc[0] = [2,5,6,7]
desired_df = df2.cumsum()