Summarise groups of rows or columns
.sum(..., character = NULL, numeric = NULL)[integerish(1)]
columns or rows that shall be combined.
If there are several items provided, they will be summarised into one group
that is combined according to its type and the respective function provided
in character or numeric.
[function(1)]
function by which character columns
or rows shall be combined.
[function(1)]
function by which numeric columns or
rows shall be combined.
the index values where the target was found.
By default character values are summarised with the function
paste0(na.omit(x), collapse = "-/-") and numeric values with
the function sum(x, na.rm = TRUE). To avoid un-intuitive behavior,
it is wisest to explicitly specify how all exceptions, such as NA-values,
shall be handled and thus to provide a new function.