# StatsModels values(Schema) no longer works

**URL:** <https://discourse.julialang.org/t/statsmodels-values-schema-no-longer-works/46659>\
**Category:** Statistics\
**Tags:** question\
**Created:** [September 15, 2020, 7:56pm UTC](https://discourse.julialang.org/t/statsmodels-values-schema-no-longer-works/46659 "2020-09-15T19:56:09Z")\
**Posts on this page:** 4\
**Page:** 1

<div class="post-metadata">

**Author:** ![Ross\_Boylan](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/ross_boylan/32/9210_2.png) [@Ross\_Boylan](https://discourse.julialang.org/u/Ross_Boylan)\
**Post date:** [September 15, 2020, 7:56pm UTC](https://discourse.julialang.org/t/statsmodels-values-schema-no-longer-works/46659/1 "2020-09-15T19:56:10Z")

</div>

About a year ago, using StatsModels 0.6.5, the following code worked:

```julia
function exploder(formula::FormulaTerm, df)
    s = schema(formula, df)
    function iscat(x)
        return isa(x, CategoricalTerm)
    end
    cats = filter(iscat, collect(values(s)))
...

```

After updating to the latest, 0.6.14, it fails:

```julia
ERROR: MethodError: no method matching length(::StatsModels.Schema)

```

My stack trace doesn’t show anything useful (because I’m in the debugger?) but by stepping through I found the problem is in `values(s)`, which leads to

```julia
collect(itr) = _collect(1:1 #= Array =#, itr, IteratorEltype(itr), IteratorSize(itr))

```

`IteratorSize` seems to lead to the call to `length`.

The docs say Schema is a subtype of Dictionary, and so it sounds as if this should work.

I don’t know if this is a bug or if I’m using the type incorrectly. Any ideas?

Thanks.

---

<div class="post-metadata">

**Author:** ![Ross\_Boylan](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/ross_boylan/32/9210_2.png) [@Ross\_Boylan](https://discourse.julialang.org/u/Ross_Boylan)\
**Post date:** [September 17, 2020, 1:22am UTC](https://discourse.julialang.org/t/statsmodels-values-schema-no-longer-works/46659/2 "2020-09-17T01:22:43Z")

</div>

Here’s a self-contained example:

```julia
using DataFrames
using StatsModels
using CategoricalArrays
df = DataFrame(a=categorical([1, 3, 4, 3]), b=["z", "a", "a", "b"], c=[0., 0.5, 1.0, 1.5])
# complex model
f = @formula(a+b ~ a*b+b*c)
s = schema(f, df)
vs = values(s)
println(vs === s)
function iscat(x)
    return isa(x, CategoricalTerm)
end
cats = filter(iscat, collect(values(s)))
foreach(println, values(s))
    println(x)
end

```

`values(s)` simply returns `s`.

The `filter` leads to

```julia
MethodError: no method matching length(::StatsModels.Schema)
Closest candidates are:
  length(!Matched::JSON.Parser.MemoryParserState) at C:\Users\rdboylan\.julia\packages\JSON\3rsiS\src\Parser.jl:28
  length(!Matched::CompositeException) at task.jl:41
  length(!Matched::LibGit2.GitBlob) at D:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.5\LibGit2\src\blob.jl:3
  ...
_similar_for(::UnitRange{Int64}, ::Type{Any}, ::StatsModels.Schema, ::Base.HasLength) at array.jl:597
_collect(::UnitRange{Int64}, ::StatsModels.Schema, ::Base.HasEltype, ::Base.HasLength) at array.jl:630
collect(::StatsModels.Schema) at array.jl:624
top-level scope at eg01.jl:12
include_string(::Function, ::Module, ::String, ::String) at loading.jl:1088

```

while the `foreach` yields

```julia
MethodError: no method matching iterate(::StatsModels.Schema)
Closest candidates are:
  iterate(!Matched::LibGit2.GitRebase) at D:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.5\LibGit2\src\rebase.jl:48
  iterate(!Matched::LibGit2.GitRebase, !Matched::Any) at D:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.5\LibGit2\src\rebase.jl:48
  iterate(!Matched::CommonMark.Node) at C:\Users\rdboylan\.julia\packages\CommonMark\tT85V\src\ast.jl:52
  ...
foreach(::typeof(println), ::StatsModels.Schema) at abstractarray.jl:2009
top-level scope at eg01.jl:9
include_string(::Function, ::Module, ::String, ::String) at loading.jl:1088

```

Julia 1.5.1.

---

<div class="post-metadata">

**Author:** ![Ross\_Boylan](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/ross_boylan/32/9210_2.png) [@Ross\_Boylan](https://discourse.julialang.org/u/Ross_Boylan)\
**Post date:** [September 17, 2020, 1:58am UTC](https://discourse.julialang.org/t/statsmodels-values-schema-no-longer-works/46659/3 "2020-09-17T01:58:49Z")

</div>

And with this addition the previous test code works:

```julia
Base.values(schema::StatsModels.Schema) = values(schema.schema)

```

This is like other definitions of other iterator/accessor-like functions already in `StatsModels.Schema`.

Why the code used to work and no longer does remains unclear. Going back to the 0.6.5 version of Schema.jl does not result in a definition of `values` that has since been removed. Perhaps there was some change in Julia’s handling of collections? The current documentation for `Base.values` does say that the default implementation returns the original object, which is what was happening before the tweak above.

---

<div class="post-metadata">

**Author:** ![Ross\_Boylan](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/ross_boylan/32/9210_2.png) [@Ross\_Boylan](https://discourse.julialang.org/u/Ross_Boylan)\
**Post date:** [September 17, 2020, 2:23am UTC](https://discourse.julialang.org/t/statsmodels-values-schema-no-longer-works/46659/4 "2020-09-17T02:23:20Z")

</div>

Opened [https://github.com/JuliaStats/StatsModels.jl/issues/193#issue-703212877](https://github.com/JuliaStats/StatsModels.jl/issues/193#issue-703212877) about the general question of how `Dict`-like `Schema` should be.