I would like to get rid off some dates in a column that are as follow (there are more than 40.000 records and I cannot go one by one):
d <- c("16/19/07/1953",
"16/19/08/1953",
"16/21/7/1/59",
"16/21/vii/1967")
I would like just to substitute these dates that have three forward slashes or more in some cases by NA. Any help or advice would be much appreciated!