Random sampling by category, different number of samples needed per category in R

I have a question to do some random sampling in R. I have two datasets. One dataset, say df1, is organized where each observation is a sample, and the location from which the sample was collected is under the variable "loc". "loc" is set as a character. An example data layout is shown below.

    ID loc x1 x2 x3 
    1  A   x  x  x
    2  A   x  x  x
    3  A   x  x  x
    4  B   x  x  x
    5  B   x  x  x 
    6  C   x  x  x 
    7  C   x  x  x 
    8  C   x  x  x
    9  C   x  x  x
    etc.

The second dataset, say df2, is a list of all of the locations and the number of random samples required from each location. It looks like this:

    loc n
    A   2
    B   1
    C   3

I am wondering how to take different numbers of random samples by group, where the number of samples required is denoted in df2.