# How to join a DataFrame by index using Pandas with Python
# To work with dataframes
import pandas as pd

# To generate data
import numpy as np

# We create a common index that we will need to join the two 
# DataFrames together
dates = pd.date_range(start="2021-01-01", end="2021-12-31")

# We create our first sample dataframe
df_sales = pd.DataFrame(index=dates, 
	data={"sales": np.abs(np.random.normal(2500, 2000, len(dates)))})

# We create our second sample dataframe
df_cogs = pd.DataFrame(index=dates, 
    data={"cogs": np.abs(np.random.normal(1100, 1000, len(dates)))})

# We join the second DataFrame to the first DataFrame.
df_combined = df_sales.join(df_cogs)

# We print the combined DataFrame 
print(df_combined)