hadley/ggplot2 — Issue #375: minor_breaks in date/date_time scale
Author: kohske
Created: 2012-01-26 00:51:28+00:00
State: open
Labels: bug

```R
df <- data.frame(
day30 = seq(Sys.Date(), length = 10, by = "5 day"),
y = runif(10)
)

p <- ggplot(df, aes(day30, y)) + geom_line()
p + scale_x_date(breaks = "2 month", minor_breaks = "week")
```

incudes an error.

```
Error in Ops.Date((x - from[1]), diff(from)) :
/ not defined for Date objects
```

Maybe this is because,
1. data are transformed into `numeric` by `scales:::from_date` in `date_trans`
2. `minor_breaks` are calculated on the original data space (i.e., `date`).
3. some arithmetic operation combines `numeric` and `date`.

Anyway it need to be reconsidered...