Incorrect outputs for the `add` example

[devcrocod]

https://kotlin.github.io/dataframe/adddf.html

Examples of input and output data for the select method

[Jolanrensen]

What's wrong about the output?

[devcrocod]

I now understand what select outputs mean. But it’s very difficult to keep track of how two dataframes are created and why select at all when we just have an example df.add(df1, df2)