I need to convert a data.frame into a list of characters based on one of the column of the dataframe.

Starting from a data.frame of two colums, the first one contains uniques values of compounds names, while the other contains compound type categories, that are not unique. Example:

```
Compound_name Compound_type
A             Inhibitor_A
B             Inhibitor_B
C             Inhibitor_A
D             Inhibitor_C
E             Inhibitor_B

```

I would like to end with a list based on the compound types that looks like this:

```
Inhibitor_A   'A' 'C'
Inhibitor_B   'B' 'E'
Inhibitor_C   'C'

```

My data.frame contains 2000 compounds, so I need a way to do it iteratively. 

I don't know where to start to compute this, so many thanks in advance.