Merging pandas dataframes with different size on column with non-unique elements

Question

I have two pandas dataframes I want to combine based on the value of a common column in the dataframe. However in one of the dataframes the values in the column are not unique:

df1 = pd.DataFrame(
{'SimId:': [1, 1, 1, 2, 2],
 'RunId': [1, 2, 3, 1, 2],
 'Velocity': [5, 6, 7, 8, 9]})

df2 = pd.DataFrame(
{'SimId': [1, 2],
 'weather': ['sun', 'snow']})

As a result I would like to get a dataframe like this:

df3 = pd.DataFrame(
{'SimId:': [1, 1, 1, 2, 2],
 'RunId': [1, 2, 3, 1, 2],
 'Velocity': [5, 6, 7, 8, 9],
 'weather': ['sun', 'sun', 'sun', 'snow', 'snow']})

When trying to merge like this:

df3 = pd.merge(df1, df2, on='SimId', how='right')

I get a "KeyError".

Can anyone help me with what is the most pythonic way to solve this?

Answer 1

Your code works:

df3 = pd.merge(df1, df2, on='SimId', how='right')

You just need to fix a typo in df1: not 'SimId:', but 'SimId'.

Answer 2

your code works as Andrey said just fix a typo in df1
df1 = pd.DataFrame(
{'SimId': [1, 1, 1, 2, 2],
'RunId': [1, 2, 3, 1, 2],
'Velocity': [5, 6, 7, 8, 9]})

 df2 = pd.DataFrame(
{'SimId': [1, 2],
'weather': ['sun', 'snow']})

df3 = pd.merge(df1, df2, on='SimId', how='right')
print (df3)
   RunId  SimId  Velocity weather
   # 0      1      1         5     sun
   # 1      2      1         6     sun
   # 2      3      1         7     sun
   # 3      1      2         8    snow
   # 4      2      2         9    snow