# JuMP: filtering the output of JuMP.value.(x)

**URL:** <https://discourse.julialang.org/t/jump-filtering-the-output-of-jump-value-x/25391>\
**Category:** Optimization (Mathematical)\
**Created:** [June 18, 2019, 8:17am UTC](https://discourse.julialang.org/t/jump-filtering-the-output-of-jump-value-x/25391 "2019-06-18T08:17:28Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![PatrickHealy](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/patrickhealy/32/8887_2.png) [@PatrickHealy](https://discourse.julialang.org/u/PatrickHealy)\
**Post date:** [June 18, 2019, 8:17am UTC](https://discourse.julialang.org/t/jump-filtering-the-output-of-jump-value-x/25391/1 "2019-06-18T08:17:29Z")

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Is there a nice idiom for filtering all of the elements of a JuMP array of binaries that are set? Even with iterating over the elements of JuMP.value.(x) in a for-loop I don’t seem to be able to catch the indices in a useful format.

Thanks.

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**Author:** ![odow](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/odow/32/28685_2.png) [@odow](https://discourse.julialang.org/u/odow)\
**Post date:** [June 18, 2019, 2:02pm UTC](https://discourse.julialang.org/t/jump-filtering-the-output-of-jump-value-x/25391/2 "2019-06-18T14:02:04Z")

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What do you mean by “set”?

The answer depends on the container of the JuMP variable.

Arrays:

```nohighlight
using JuMP, GLPK
model = Model(with_optimizer(GLPK.Optimizer))
@variable(model, x[1:2, 1:2], Bin)
optimize!(model)
filter(k -> value(x[k]) > 0.5, keys(x))

```

`Containers.DenseAxisArray`:

```nohighlight
using JuMP, GLPK
model = Model(with_optimizer(GLPK.Optimizer))
@variable(model, x[1:2, [:A, :B]], Bin)
optimize!(model)
# The following doesn't work for some reason
filter(k -> value(x[k]) > 0.5, keys(x))
# Here is a work-around
filter(k -> value(x[k]) > 0.5, collect(keys(x)))

```

`Containers.SparseAxisArray`:

```nohighlight
using JuMP, GLPK
model = Model(with_optimizer(GLPK.Optimizer))
@variable(model, x[i=1:2, j=i:2], Bin)
optimize!(model)
# The following doesn't work: it appears to be a bug.
filter(k -> value(x[k]) > 0.5, keys(x))
# Here is a work-around
filter(k -> value(x[k]) > 0.5, collect(keys(x.data)))

```

I’ll open an issue in JuMP: [Unify treatment of `keys` on JuMP containers. · Issue #1988 · jump-dev/JuMP.jl · GitHub](https://github.com/JuliaOpt/JuMP.jl/issues/1988)

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<div class="post-metadata">

**Author:** ![PatrickHealy](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/patrickhealy/32/8887_2.png) [@PatrickHealy](https://discourse.julialang.org/u/PatrickHealy)\
**Post date:** [June 18, 2019, 3:51pm UTC](https://discourse.julialang.org/t/jump-filtering-the-output-of-jump-value-x/25391/3 "2019-06-18T15:51:06Z")

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Sorry, that’s the electrical engineer coming out in me 😉

Here’s what I got following your suggestions:

```julia
julia> typeof(x)
JuMP.Containers.DenseAxisArray{VariableRef,1,Tuple{Array{Tuple,1}},Tuple{Dict{Tuple,Int64}}}

julia> collect(keys(x))
ERROR: MethodError: Cannot `convert` an object of type JuMP.Containers.DenseAxisArrayKey{Tuple{Tuple{Int64,Int64}}} to an object of type JuMP.Containers.DenseAxisArrayKey{Tuple{Tuple}}
Closest candidates are:
  convert(::Type{S}, ::T< .....
    :

julia> keys(x)
JuMP.Containers.DenseAxisArrayKeys{Tuple{Array{Tuple,1}}}(Base.Iterators.ProductIterator{Tuple{Array{Tuple,1}}}((Tuple[(1, 4), (4, 1), (1, 10), (10, 1), (1, 12), (12, 1), (1, 14), (14, 1), (1, 18), (18, 1) … (45, 48), (48, 45), (45, 50), (50, 45), (46, 49), (49, 46), (47, 48), (48, 47), (47, 50), (50, 47)],)))
julia> filter(k -> value(x[k]) > 0.5, keys(x))
ERROR: MethodError: no method matching filter(::getfield(Main, Symbol("##1067#1068")), ::JuMP.Containers.DenseAxisArrayKeys{Tuple{Array{Tuple,1}}})
Closest candidates are:
  filter(::Any, ::Array{T,1} where T) at array.jl:2351
  filter(::Any, ::BitArray) at bitarray.jl:1710
  filter(::Any, ::AbstractArray) at array.jl:2312
  ...

```

Not sure if I’m doing something wrong here. Thanks.

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<div class="post-metadata">

**Author:** ![odow](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/odow/32/28685_2.png) [@odow](https://discourse.julialang.org/u/odow)\
**Post date:** [June 18, 2019, 4:42pm UTC](https://discourse.julialang.org/t/jump-filtering-the-output-of-jump-value-x/25391/4 "2019-06-18T16:42:48Z")

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Please provide a minimum working example. See: [Please read: make it easier to help you](https://discourse.julialang.org/t/psa-make-it-easier-to-help-you/14757)

Do the ones above work for you?