DataFrame 的衍生物

Question

I am working with two dataframes, let's name them time and voltage, and their shape is [2201 rows x 8 columns].

The first and last rows of the dataframes are (time and voltage respectively):

               A = 2.90 V           A = 3.00 V           A = 3.10 V           A = 3.20 V           A = 3.30 V           A = 3.40 V           A = 3.50 V           A = 4.90 V
0            0.000000e+00         0.000000e+00         0.000000e+00         0.000000e+00         0.000000e+00         0.000000e+00         0.000000e+00         0.000000e+00
1            2.000000e-09         2.000000e-09         2.000000e-09         2.000000e-09         2.000000e-09         2.000000e-09         2.000000e-09         2.000000e-09
2            4.000000e-09         4.000000e-09         4.000000e-09         4.000000e-09         4.000000e-09         4.000000e-09         4.000000e-09         4.000000e-09
3            6.000000e-09         6.000000e-09         6.000000e-09         6.000000e-09         6.000000e-09         6.000000e-09         6.000000e-09         6.000000e-09
4            8.000000e-09         8.000000e-09         8.000000e-09         8.000000e-09         8.000000e-09         8.000000e-09         8.000000e-09         8.000000e-09
...                   ...                  ...                  ...                  ...                  ...                  ...                  ...                  ...
2196         4.392000e-06         4.392000e-06         4.392000e-06         4.392000e-06         4.392000e-06         4.392000e-06         4.392000e-06         4.392000e-06
2197         4.394000e-06         4.394000e-06         4.394000e-06         4.394000e-06         4.394000e-06         4.394000e-06         4.394000e-06         4.394000e-06
2198         4.396000e-06         4.396000e-06         4.396000e-06         4.396000e-06         4.396000e-06         4.396000e-06         4.396000e-06         4.396000e-06
2199         4.398000e-06         4.398000e-06         4.398000e-06         4.398000e-06         4.398000e-06         4.398000e-06         4.398000e-06         4.398000e-06
2200         4.400000e-06         4.400000e-06         4.400000e-06         4.400000e-06         4.400000e-06         4.400000e-06         4.400000e-06         4.400000e-06

[2201 rows x 8 columns]
               A = 2.90 V           A = 3.00 V           A = 3.10 V           A = 3.20 V           A = 3.30 V           A = 3.40 V           A = 3.50 V           A = 4.90 V
0                0.003537             0.007219             0.012674             0.017294             0.022206             0.027240             0.032120             0.106918
1                0.003532             0.007214             0.012666             0.017288             0.022212             0.027280             0.032082             0.106855
2                0.003537             0.007217             0.012677             0.017342             0.022264             0.027290             0.032008             0.106764
3                0.003535             0.007221             0.012671             0.017352             0.022236             0.027307             0.032054             0.106809
4                0.003539             0.007224             0.012675             0.017336             0.022244             0.027320             0.032064             0.106836
...                   ...                  ...                  ...                  ...                  ...                  ...                  ...                  ...
2196             0.000399             0.000490             0.000579             0.000164             0.000176             0.000230             0.000238             0.000336
2197             0.000406             0.000495             0.000578             0.000146             0.000216             0.000237             0.000252             0.000227
2198             0.000405             0.000495             0.000577             0.000188             0.000192             0.000273             0.000230             0.000264
2199             0.000402             0.000494             0.000573             0.000138             0.000216             0.000193             0.000240             0.000200
2200             0.000408             0.000492             0.000572             0.000170             0.000210             0.000253             0.000224             0.000373

I can eaily plot the curves for each column (voltage vs time). I would like to get the derivative of the voltage dataframe respect the time dataframe, or what it is the same in mathemetics (dvoltage/dtime) and then plot (dvoltage/dtime) vs time.

I have tried the following code:

def Derivative():
    dV_dt = []
    for c in range(len(V.columns)):
        dn = derivative(V.iloc[:,c], time.iloc[:,c], dx=time.iloc[:,c])
        dV_dt.append(dn)
    dV_dt = pd.DataFrame(dV_dt)
    print(dV_dt)

raising the following error:

  File "C:\ProgramData\Anaconda3\Lib\site-packages\scipy\misc\common.py", line 119, in derivative
    val += weights[k]*func(x0+(k-ho)*dx,*args)
TypeError: 'Series' object is not callable

Does anyone how to solve this? Thanks in advance.

Answer 1

You can try the following:

import pandas as pd
import numpy as np
V = pd.DataFrame(np.random.rand(2201, 8)*10)
time = pd.DataFrame(np.random.rand(2201, 8))
dV_dt = pd.DataFrame([np.diff(V[i])/np.diff(time[i]) for i in V.columns])
print (V,time,dV_dt)

please note the the resultant dV_dt is one row less (2200 rows only) than the original two dataframes. as the derivative is taken between two consequential values.