[R] median of grouped data

["María del Pilar Márquez"]

Good morning,
I would like to know if is possible somebody can help me with this please:
I would like to calculate the median of grouped data, this is an example:

ID    PM
adt_01  25.255
adt_01  225.36
adt_01  14.2325
adt_02  15
adt_02  12.3
adt_03  15.2
adt_03  148.3
adt_03  25.5
adt_03  14.25

I need the median of adt_01, 02 and 03 , I know that I have to split first my data and then ask for the median but the code I have is not working.

Thank you very much if you can help me with the code
maria