다 그러다

'They said…' / 'if you say…'

This is -다고 그러다 with the 고 dropped in speech. Looking back, it relays what someone said: 여기 등심돈가스도 맛있다 그러던데? 'I hear the pork cutlet here is good too.' Looking forward, it sets up a case in an explanation — 예를 들면 여러분들이 성수에 지내고 있다 그러면 'say, for example, you're staying in Seongsu.' Both uses are conversational; writing keeps the 고.

Register: casual spoken