Merge two dataframe columns into one column with a second column containing their labels [duplicate]

This may be similar to the pivot function but I'm not sure if it applies in this case:

If I have a df:

  date x1 x2
1 1-01 a  b 
2 1-01 c  d
3 1-02 e  f
4 1-02 g  h
5 1-03 i  j

Can I combine the x1 and x2 column into this:

   date  combined type
1  1-01  a        x1 
2  1-01  b        x2
3  1-01  c        x1 
4  1-01  d        x2
5  1-02  e        x1
6  1-02  f        x2
7  1-02  g        x1
8  1-02  h        x2
9  1-03  i        x1
10 1-03  j        x2

I tried using paste (e.g. df <- paste(df$x1,df$x2)) but I lose out on the labels. I'm not sure if I can incorporate the pivot_longer function into a mutate statement in my ggplot statement.