Calculating the percentage change by year for a particular column

Question

Suppose I have this dataframe

data = {'Year': ['2010', '2011', '2012'],
        'Total_Population': [1000, 1200, 1600]}
df_sample = pd.DataFrame(data=data)
df_sample.head()

I want to calculate the percentage change in Year for Total_Population. I tried following this here. Which boiled down to this code

cols1 = ['Year', 'Total_Population']
vals = df[cols1].merge(df.assign(year=df['Year']+1), on=cols1, how='left')['values']
df['change_in_population'] = df['values'].sub(vals).div(vals).mul(100).fillna(0)

For the actual .csv file the size is about 215.2 MB and when I try the latter my memory blows up and I have 64 gb of RAM. Is there a better way of doing this?

Asked By: Wolfy

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Source

Answer 1

Did you try pct_change?

df_sample['% change'] = df_sample['Total_Population'].pct_change() * 100
print(df_sample)

Output:

   Year  Total_Population   % change
0  2010              1000        NaN
1  2011              1200  20.000000
2  2012              1600  33.333333

Answered By: Bill

Calculating the percentage change by year for a particular column

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