rolling up a string

i have a string field (bill to name)

i would like to take the following and foll it up to one value

abc industries

abc international

abc industries international

i would like them to all be grouped by ABC

i have tried

if instr({string field},"/")>0 then

split({string field},"/") [1]

i receive an error THIS ARRAY MUST BE SUBSCRIPTED for example ARRAY <i>,

im a bit confused can anyone tell me how to get this to work please, not familar with arrays.