Filters manipulate sets of titles in which no title may appear more than once. Furthermore, they often need to append one such set to another.
This is done in such a way that, if a title would be duplicated, the earlier copy of that title is discarded. The titles being appended are dominant.
For example, if a selection contains Andrew Becky Clara Daniel
and Andrew Barney Clara Daisy
is then appended to it, the result is Becky Daniel Andrew Barney Clara Daisy
.
This behaviour can cause unexpected results when working with Mathematics Operators. For example, 1 2 3 +[sum[]]
evaluates to 6
, as expected. But 1 1 1 +[sum[]]
evaluates to 1
. Removing the +[sum[]]
from each filter reveals the problem: 1 2 3
evaluates to the list 1
, 2
, 3
, while 1 1 1
evaluates to the single item 1
due to de-duplication.
In such situations, the =
prefix can be used to disable the de-duplication. For example, =1 =1 =1 +[sum[]]
evaluates to 3
as expected. Alternatively, the split Operator can be used: [[1,1,1]split[,]sum[]]
.