Compare quantity of each item in dataframe in pandas-CodePudding

I fairly new to programming in python and using the pandas library and I am having problems with comparing 2 dataframes with different quantities i want to see if the quantity in data_1 is less than the quantity in data_2 for each item

import pandas as pd

data_1 = [['banana',10],['orange',2],['strawberry',3]]
data_2 = [['banana',1],['orange',2],['strawberry',5],['melon',8]]

df_1 = pd.Dataframe(data_1,columns = ['item','quantity'])
df_2 = pd.Dataframe(data_2,columns = ['item','quantity'])

i was trying to use pd.merge() the 2 dataframes to compare but it's not quite what i was looking for..... i needed a 3° dataframe with the differences only

CodePudding user response：

For such comparison item should be index and then you might concat quantity columns and compute desired column following way

import pandas as pd

data_1 = [['banana',10],['orange',2],['strawberry',3]]
data_2 = [['banana',1],['orange',2],['strawberry',5],['melon',8]]

df_1 = pd.DataFrame(data_1,columns = ['item','quantity'])
df_2 = pd.DataFrame(data_2,columns = ['item','quantity'])

df = pd.concat({"data1":df_1.set_index("item").quantity,"data2":df_2.set_index("item").quantity},axis=1,sort=False)
df['isless'] = df['data1'] < df['data2']
print(df)

output

            data1  data2  isless
banana       10.0      1   False
orange        2.0      2   False
strawberry    3.0      5    True
melon         NaN      8   False