心不在焉

absent-minded / preoccupied / inattentive / with one's thoughts wandering

heart / mind / intention / center / core / CL:顆|颗[ke1],個|个[ge4]

no; not so / (bound form) not; un-

not to be present / to be out / (euphemism) to pass away / to be deceased

to exist; to be alive / (of sb or sth) to be (located) at / (used before a verb to indicate an action in progress)

where / how