小编las*_*r.p的帖子

我有一个看起来像这样的数据表：

Property    Type
1           apartment
1           office
2           office
2           office
3           apartment
3           apartment
3           office

我现在想按财产计算办公室和公寓：

Property    Type       number_of_offices    number_of_apartments
       1    apartment                  1                       1
       1    office                     1                       1
       2    office                     2                       0
       2    office                     2                       0
       3    apartment                  1                       2
       3    apartment                  1                       2
       3    office                     1                       2

我试过

my.DT <- myDT[,.(Type=Type, number_of_offices=nrow(my.DT[my.DT$Type=="office",]), number_of_apartments=nrow(my.DT$Type=="apparment",], by="Property")

但是，这只给了我整个数据表的总数。有没有人有办法解决吗？