Calculate summary statistics from a data frame by group. Currently supports the mean, median and standard deviation.

`calc_summary_stats(samples, summarise_by = c())`

- samples
A data.table containing at least a value variable

- summarise_by
A character vector of variables to group by.

A data.table containing the upper and lower bounds for the specified credible interval

```
samples <- data.frame(value = 1:10, type = "car")
# default
calc_summary_stats(samples)
#> median mean sd
#> 1: 5.5 5.5 3.02765
# by type
calc_summary_stats(samples, summarise_by = "type")
#> type median mean sd
#> 1: car 5.5 5.5 3.02765
```