maintain attributes of intervals when using Reduce

[mgacc0]

I want to obtain the union of many (more than 2) intervals:

df <- data.frame(id=c(1, 2, 3),
             interval=c(
               new_interval(ymd("2001-01-01"), ymd("2002-01-01")),
               new_interval(ymd("2001-01-01"), ymd("2004-01-01")),
               new_interval(ymd("2001-02-01"), ymd("2002-01-01"))
               ))
df
#   id                       interval
#1  1 2001-01-01 UTC--2002-01-01 UTC
#2  2 2001-01-01 UTC--2004-01-01 UTC
#3  3 2001-02-01 UTC--2002-01-01 UTC

lubridate::union(lubridate::union(df$interval[1], df$interval[2]),
                 df$interval[3])
# [1] 2001-01-01 UTC--2004-01-01 UTC

That's the correct result.

But why lubridate::union does not work with Reduce?

Reduce(lubridate::union, df$interval )
# [1] 31536000 94608000 28857600

The intervals objects seem to get converted to numeric too son (before applying the union).

Related to: http://stackoverflow.com/questions/32944273/lubridate-how-to-calculate-the-union-of-many-intervals

[vspinu]

Reduce calls as.list on the input, so that lubridate's union is not even called on those inputs.

There are two approaches, either extend union to accept additional arguments and handle this case internally, or implement as.list( method for interval objects.

[mgacc0]

Thanks