用 Pandas 中的前一行列填充当前行和列值

Question

I have set of readings and I need current and previous value to measure some parameters. How do I populate easily in pandas such that current row, column value takes from previous row, column value. If prev row,col doesn't exit, then I want to fill with -1 or na or anything.

 events  = np.array([[  3.,   -1., 441., 780.,  30., 262.,   0.,   0.,   0.,  -1.],
       [  4.,   3., 437., 770.,  30., 274.,   0.,   0.,   0.,  -1.],
       [  5.,   4, 431., 754.,  31., 286.,   0.,   0.,   0.,  -1.]]) 

df=pd.DataFrame(data=events, columns=["curr", "expected_prev", "f1", "f2", "f3", "f4", "f5", "f6", "f7","prev"])

For example, I want to fill values in panda dataframe as below. The below expected_prev is hardcoded, how do I generate or fill the prev column in pandas.

Answer 1

Check with shift

df['exp_pre'] = df['curr'].shift().fillna(-1)