# Merge

### Description
Finds all items in `A` for which the second column matches an object from `B`.
Usually used to merge back objects which have previously been split.

### Input
- `A [OBJ,OBJ]`: a list of pairs to be searched
- `B [OBJ]`: a list of objects to be found in `A`

### Output
- `A1 [OBJ]`: from the first column of `A` only those items of which the second column matched with `B`
- `A1A2 [OBJ,OBJ]`: tuples of `A` where the second column matched with `B`
- `A1B1 [OBJ,OBJ]`: tuples `(A1,B)` where `A2` matched with `B`

Output scores can be [aggregated](docs://score_aggregation) and/or [normalised](docs://score_normalisation).