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Handy functions from dplyr #192
Description
Going through the dplyr manual, I see several functions that might add to query. These include sample, bind_rows, bind_cols, rename, mutate, slice, n, and top_n. I'm not sure if they are all necessary, but some of them might be nice and I could pitch in here.
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bramtayl commentedon Aug 24, 2018
Oh and all the different joins too
davidanthoff commentedon Sep 1, 2018
YES! I think that is actually the area where we could add the most value right now to Query.jl.
I have thought a lot about
mutateand to some degreeselect, and not at all about the others. Here is my current thinking:First, I think we should try to implement all the
mutateandselectvariants in the front end only. I think it should be feasible that they all end up as@mapcalls under the hood, and in that way we actually don't have to add anything to QueryOperators.jl, or do any work on the backends.Then, I think we could probably as a first step try to add features like that as new functions that manipulate
NamedTuples, so that they can be used from within@map, before we start to add helper functions like@mutateand@select.I think for starters, if we had a type stable
mergefunction forNamedTuples, it would go a long way. Saymerge((a=1,b=2),(c=3))==(a=1,b=2,c=3). Once we have that, we could add some syntax to{}to make it easier to use that. For example{a..., b..., x=3}could be translated tomerge(a, b, (x=3,))in the various Query.jl macros.Another area would be selecting subsets of columns. We could either have something like
startswith((foo1=1, bar=2, foo2=3), :foo)==(foo1=1,foo2=3), or something like(foo1=1, bar=2, foo2=3)[startswith(:foo)]==(foo1=1,foo2=3). I'm not sure which of these is better. In a query it might look like@map(startswith(_, :foo))or@map(_[startswith(:foo)]). I think I like the first one better, but not sure... The second approach would be more in line with this, which probably would also be worthwhile... In general I think we need a lot more features to select columns, but we probably should iterate a bit with various designs?Maybe as a first step I should create queryverse/NamedTupleHelpers.jl, where we could play with some of these methods, and where they could have their home?