[R] Recoding multiple TRUE/FALSE columns into a single list of TRUE columns

[David Epstein]

Hi everyone,

I need to recode multiple columns in a dataframe into a single column in a
variety of different ways.  Often the values will be TRUE/FALSE and I want a
list of the columns that are true as in the Result column below:
 
    P1   P2   P3   P4   Result   
1   0    0    1    1    P3,P4
2   0    1    1    1    P2,P3,P4
3   1    0    0    0    P1
4   0    0    0    0    NA
5   1    1    1    1    P1,P2,P3,P4

I'm still relatively new to R and tend to think in for loops. I'm sure there
exists a more concise and elegant solution. Any advice?

Happy holidays,
-david