Python integration of Pandas dataframe

Question

I have the following pandas dataframe df with 2 columns, which looks like:

I would like to integrate the area under this curve if we were to plot the first columns as the x-axis and the second column as the y-axis. I have tried doing this using the integrated module from scipy (from scipy import integrate), and applied as follows as I have seen in examples online:

print(df.integrate)

However, it seems the integrate function does not work. I'm receiving the error:

Dataframe object has no attribute integrate

How would I go about this?

Thank you

James · Accepted Answer · 2021-04-22 13:21:28Z

1

You want numerical integration given a fixed sample of data. The Scipy package lists a handful of methods to do this: https://docs.scipy.org/doc/scipy/reference/integrate.html#integrating-functions-given-fixed-samples

For your data, the trapezoidal is probably the most straight forward. You provide the y and x values to the function. You did not post the column names of your data frame, so I am using the 0-index for x and the 1-index for y values

from scipy.integrate import trapz

trapz(df.iloc[:, 1], df.iloc[:, 0])

answered Apr 22, 2021 at 13:21

James

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1 Comment

thereiswaldo Over a year ago

Thanks for your answer! I have applied your code as listed above (my x-axis is 'time' and y-axis is 'fuel', they are both strings I believe). When running the following line: print (trapz(df.iloc[:,'fuel [m3'], df.iloc[:, 'time [s]'])) I get the following ValueError however: Location based indexing can only have [integer, integer slice (START point is INCLUDED, END point is EXCLUDED), listlike of integers, boolean array] types

drew_psy · Accepted Answer · 2021-04-22 13:18:03Z

0

Since integrate is a scipy method not a pandas method, you need to invoke it as follows:

from scipy.integrate import trapz, simps
print(trapz(*args))

https://docs.scipy.org/doc/scipy/reference/tutorial/integrate.html

answered Apr 22, 2021 at 13:18

drew_psy

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2 Comments

thereiswaldo Over a year ago

Thanks for you answer and the link. My question now is how do I get the first column as x-axis and second as y-axis in for example a list? I need to do this right to perform the following: integral = simps(y,x) as per the example in your link?

drew_psy Over a year ago

df['x'].to_list() OR df.x.values, the first one gives you a list the second is pandas native method.

Rishin Rahim · Accepted Answer · 2021-04-22 13:27:29Z

0

Try this

import pandas as pd
import numpy as np

def integrate(x, y):
    area = np.trapz(y=y, x=x)
    return area

df = pd.DataFrame({'x':[0, 1, 2, 3, 4, 4, 5],'y':[0, 1, 3, 3, 5, 6, 7]})
x = df.x.values
y = df.y.values
print(integrate(x, y))

answered Apr 22, 2021 at 13:27

Rishin Rahim

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2 Comments

thereiswaldo Over a year ago

Thanks for your answer! However, with this method I need to fill in the x and y axis by hand, but what if these values are a very big column? How would I get the x and y axes separately from the dataframe?

Rishin Rahim Over a year ago

The dataframe mentioned is just a sample pandas dataframe. You can get the column values with df['col_name'].values (replace column name with your x values or y values columns)

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