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remove confusing meta_table example #231

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Jun 17, 2022
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remove confusing meta_table example #231

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35 changes: 0 additions & 35 deletions docs/src/advanced.md
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Expand Up @@ -91,41 +91,6 @@ julia> sa.b
2
```

In the above example, our `MyType` was composed of `data` of type `Float64` and `rest` of type `NamedTuple`. In many practical cases where there are custom types involved it's hard for StructArrays to automatically widen the types in case they are heterogeneous. The following example demonstrates a widening method in that scenario.

```julia
using Tables

# add a source of custom type data
struct Location{U}
x::U
y::U
end
struct Region{V}
area::V
end

s1 = MyType(Location(1, 0), place = "Delhi", rainfall = 200)
s2 = MyType(Location(2.5, 1.9), place = "Mumbai", rainfall = 1010)
s3 = MyType(Region([Location(1, 0), Location(2.5, 1.9)]), place = "North India", rainfall = missing)

s = [s1, s2, s3]
# Now if we try to do StructArray(s)
# we will get an error

function meta_table(iter)
cols = Tables.columntable(iter)
meta_table(first(cols), Base.tail(cols))
end

function meta_table(data, rest::NT) where NT<:NamedTuple
F = MyType{eltype(data), StructArrays.eltypes(NT)}
return StructArray{F}(; data=data, rest...)
end

meta_table(s)
```

The above strategy has been tested and implemented in [GeometryBasics.jl](https://github.com/JuliaGeometry/GeometryBasics.jl).

## Mutate-or-widen style accumulation
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