cylondude - 4 months ago 41

R Question

I am trying to order time stamps with dplyr and lubridate but I'm not getting my expected ordering.

`library(lubridate);library(dplyr)`

foo <- data.frame(time = ymd_hms(c("2016-08-31 13:40:00", "2016-08-31 06:40:00", "2016-08-31 10:40:00")),

expected_order = c(3,1,2))

foo %>% mutate(dplyr_ordered = order(time))

Answer

You confused what the `order`

and `rank`

do, from `?order`

:

order returns a permutation which rearranges its first argument into ascending or descending order.

`order`

does not return a rank of the actual value but an index vector which can be used to sort the vector, compare the following result:

```
foo %>% mutate(dplyr_order = order(time), dplyr_rank = rank(time))
# time expected_order dplyr_order dplyr_rank
# 1 2016-08-31 13:40:00 3 2 3
# 2 2016-08-31 06:40:00 1 3 1
# 3 2016-08-31 10:40:00 2 1 2
```

The result from `rank`

is what you are expecting. The result from `order`

tells you that the second element in time is smallest, followed by the third element and the first element is the largest.