# \[ANN\] DataFrameIntervals.jl — joins on intervals of time

**URL:** <https://discourse.julialang.org/t/ann-dataframeintervals-jl-joins-on-intervals-of-time/84190>\
**Category:** Package Announcements\
**Tags:** dataframes\
**Created:** [July 13, 2022, 6:47pm UTC](https://discourse.julialang.org/t/ann-dataframeintervals-jl-joins-on-intervals-of-time/84190 "2022-07-13T18:47:42Z")\
**Posts on this page:** 1\
**Showing post:** 19

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**Author:** ![aplavin](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/aplavin/32/222056_2.png) [@aplavin](https://discourse.julialang.org/u/aplavin)\
**Post date:** [July 16, 2022, 6:51am UTC](https://discourse.julialang.org/t/ann-dataframeintervals-jl-joins-on-intervals-of-time/84190/19 "2022-07-16T06:51:02Z")

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I’m not totally sure what you mean by “lazy” joins and join groups. Can you elaborate? I’m all for efficiency (:

Grouping was one of the first features added to `FlexiJoins`, was already present when I originally announced at [[ANN] FlexiJoins.jl: fresh take on joining datasets](https://discourse.julialang.org/t/ann-flexijoins-jl-fresh-take-on-joining-datasets/79655). It groups either by the left or the right-hand side. For example, grouping by the left side turns the default flat list of matches `[(1, 1), (1, 2), (1, 3), (3, 1)]` into `[(1, [1, 2, 3]), (2, []), (3, [1])]`.

All join results are `view`s of the original datasets, no matter if flat/grouped. Is this what you refer to as “lazy”? However, indices of matches are always computed eagerly, don’t think there is a way around that.

For now, grouped results work with many collections and tables, except for DataFrames. They have a very different interface compared to other collections, so `FlexiJoins` grouping doesn’t work with them as-is. I believe the potential DataFrames support is easy to implement, but not sure what the reasonable interface should be. I don’t really encounter DataFrames myself, and don’t know what kind of return type their users would expect from a grouped join.

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