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

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Here’s a possible solution using the new “non-equi” joins in data.table (v>=1.9.8). While I doubt you’ll like the syntax, it should be very efficient soluion.

Also, regarding findInterval, this function assumes continuity in your intervals, while this isn’t the case here, so I doubt there is a straightforward solution using it.

library(data.table) #v1.10.0
setDT(intervals)[data.table(elements), on = .(start <= elements, end >= elements)]
#    phase start end
# 1:     a   0.1 0.1
# 2:     a   0.2 0.2
# 3:     a   0.5 0.5
# 4:    NA   0.9 0.9
# 5:     b   1.1 1.1
# 6:     b   1.9 1.9
# 7:     c   2.1 2.1

Regarding the above code, I find it pretty self-explanatory: Join intervals and elements by the condition specified in the on operator. That’s pretty much it.

There is a certain caveat here though, start, end and elements should be all of the same type, so if one of them is integer, it should be converted to numeric first.

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