The bug occured when applying
```
ranking=challenge%>%rankThenAggregate(FUN = median,
ties.method = "min"
)
```
The data contains metric values in which small values are better. The error occurs when creating the report:
```
Quitting from lines 270-271 (chaos_vol.Rmd)
Error in object[[by]] == combinations[it, 2] :
comparison of these types is not implemented
```