Find which interval row in a data frame that each element of a vector belongs in

Question

I have a vector of numeric elements, and a dataframe with two columns that define the start and end points of intervals. Each row in the dataframe is one interval. I want to

Answer 1

David Arenburg's mention of non-equi joins was very helpful for understanding what general kind of problem this is (thanks!). I can see now that it's not implemented for dplyr. Thanks to this answer, I see that there is a fuzzyjoin package that can do it in the same idiom. But it's barely any simpler than my map solution above (though more readable, in my view), and doesn't hold a candle to thelatemail's cut answer for brevity.

For my example above, the fuzzyjoin solution would be

library(fuzzyjoin)
library(tidyverse)

fuzzy_left_join(data.frame(elements), intervals, 
                by = c("elements" = "start", "elements" = "end"), 
                match_fun = list(`>=`, `<=`)) %>% 
  distinct()

Which gives:

    elements phase start end
1      0.1     a     0   0.5
2      0.2     a     0   0.5
3      0.5     a     0   0.5
4      0.9      NA    NA
5      1.1     b     1   1.9
6      1.9     b     1   1.9
7      2.1     c     2   2.5