Comparison Operators for date_xx
# S3 method for date_xx Ops(e1, e2)
| e1, e2 | Objects with the same   | 
    
|---|
a logical scalar
#> [1] TRUE#> [1] TRUE#> Error : Comparison of <date_xx> is only defined if both objects have the same subclass, but 'e1' is <date_yq> and 'e2' is <date_ym>