Creating charts with custom function

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Hi Team,

First Streamlit is amazing and i am going to be using it extensively. I have started using but stuck at one place.

1). I have a dataframe which i has columns. The app has to display all the columns and the user can select those columns and the plot has to be generated.
2). The plot i am developing is a custom made plot with rules inside it.

Questions. how can i pass my custom function using streamlit to generate chart?

Please help.