unify(c(1,1,1,1))
#unify(c(1,1,2,1)) #warning
library(dplyr)
x=tibble(id=rep(letters[1:5],10), value=rep(1:5,10))
x %>% group_by(id) %>% summarise(value=unify(value)) #safer than `value=value[1]`
x$value[2]=1
#x %>% group_by(id) %>% summarise(value=unify(value)) #warning about that non-unique value
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