MERGE (TSOURCE, FSOURCE, MASK)

Merge under mask 

PACK (ARRAY, MASK [, VECTOR])

Pack an array into an array of rank one under a mask 

SPREAD (SOURCE, DIM, NCOPIES)

Replicates array by adding a dimension 

UNPACK (VECTOR, MASK, FIELD)

Unpack an array of rank one into an array under a mask