Turn a vector of length N to a vector of length 1 after checking that there is only one unique value. Useful to safely flatten a duplicated table. This preserves the label attribute if set.
Examples
unify(c(1,1,1,1))
#> [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]`
#> # A tibble: 5 × 2
#> id value
#> <chr> <int>
#> 1 a 1
#> 2 b 2
#> 3 c 3
#> 4 d 4
#> 5 e 5
x$value[2]=1
#x %>% group_by(id) %>% summarise(value=unify(value)) #warning about that non-unique value