[R] Lowest year among several variables

[Jeff]

...still new to R and trying to figure this one out.

I have a number of variables x, y, z, etc. in a data frame.

Each contains a 2 digit year (e.g., 80, 81, 82) representing the 
first year that something occurred. Each variable represents a 
different type of event.

If the event did not occur at all, the variable has the value 0 (zero).

I need to create a new variable having the value of the earliest year 
among the set of variables.

If none of the events occurred (all variables = 0), then the new 
variable should also be zero.

e.g.,

Original
x    y   z
80 82 83
85  76  90
90  0   86
0   0   0


New variable
80
76
86
0