Hi everybody I am trying to solve a problem in R. I want to aggregate data in R that has a `date` variable, a `character` variable and a `numeric` variable. The structure of my database is like this:

```
Date          ID         Mount
01/05/2013    1100        100
01/05/2013    1100        500
01/05/2013    11300       200
01/05/2013    11300       500
19/09/2013    4500        1000
19/09/2013    4500        3000
19/09/2013    5679        200
19/09/2013    5679        300
20/09/2013    4519        1000
20/09/2013    4519        2000
20/09/2013    5001        200
20/09/2013    5001        200

```

I want to aggregate my database first by date and second by ID, something like this:

```
Date         ID     Mount
01/05/2013   1100    600
             11300   700
19/09/2013   4500    4000
             5679    500 
20/09/2013   4519    3000
             5001    400

```

I was trying with `aggregate()` function but it only gives me `date` and `mount` and I can't put `ID` variable. Thanks for your help.