如何计算两个值之间的百分比变化？

Question

I have this dataframe with the total population number by year.

import pandas as pd
cases_df = pd.DataFrame(data=cases_list, columns=['Year', 'Population', 'Nation'])
cases_df.head(7)



 Year       Population       Nation
0   2019    328239523   United States
1   2018    327167439   United States
2   2017    325719178   United States
3   2016    323127515   United States
4   2015    321418821   United States
5   2014    318857056   United States
6   2013    316128839   United States

I want to calculate how much the population has increased from the year 2013 to 2019 by calculating the percentage change between two values (2013 and 2019):

{[(328239523 - 316128839)/ 316128839] x 100 }

How can I do this? Thank you very much!!

ps. some advice to remove index? 0 1 2 3 4 5 6

i tried to to that

df1 = df.groupby(level='Population').pct_change() 
print(df1)

but i get error because "Population" says that is not the name of Index

Answer 1

I would do it following way

import pandas as pd
df = pd.DataFrame({"year":[2015,2014,2013],"population":[321418821,318857056,316128839],"nation":["United States","United States","United States"]})
df = df.set_index("year")
df["percentage"] = df["population"] * 100 / df["population"][2013]
print(df)

output

      population         nation  percentage
year
2015   321418821  United States  101.673363
2014   318857056  United States  100.863008
2013   316128839  United States  100.000000

Note I used subset of data for brevity sake. Using year as index allow easy access to population value in 2013, percentage is computed as (population) * 100 / (population for 2013).

Answer 2

How to remove the mentioned index:

df.set_index('Year',inplace=True)

Now Year will replace your numbered index.

Now

Use cases_df.describe() or cases_df.attribute_name.describe()

Answer 3

This is more of a math question rather than a programming question.

Let's call this a percentage difference between two values since population can vary both ways (increase or decrease over time).

Now, lets say that in 2013 we had 316128839 people and in 2019 we had 328239523 people:

a = 316128839
b = 328239523

Before we go about calculating the percentage, we need to find the difference between the b and a :

diff = b - a

Now that we have that, we need to see what is the percentage of diff of a :

perc = (diff / a) * 100

And there is your percentage variation between a and b