head(date)
  year month day
1 1977     7  16
2 1977     8  19
3 1977     9  13
4 1977    10  16
5 1977    11  12
6 1977    11  12

head(date)
# A tibble: 6 x 3
   year month   day
  <int> <int> <int>
1  1977     7    16
2  1977     8    19
3  1977     9    13
4  1977    10    16
5  1977    11    12
6  1977    11    12