I would like to copy a column from a DataFrame into a new column. The Problem is that it is containing sets.

```
xy=pd.DataFrame(columns=[2])
xy.at[1,2]={1,2,3,4}
xy[3]=xy[2].copy()
xy.at[1,3].add(5)

```

I would like to get this:

```
           2                 3
1   {1, 2, 3, 4}      {1, 2, 3, 4, 5}

```

But xy is returning this:

```
           2                 3
1   {1, 2, 3, 4, 5}   {1, 2, 3, 4, 5}

```

How could I Keep the set in column 2 unchanged?
Thanks