# Convert array to dictionary

**URL:** <https://discourse.julialang.org/t/convert-array-to-dictionary/15494>\
**Category:** New to Julia\
**Created:** [September 26, 2018, 12:17am UTC](https://discourse.julialang.org/t/convert-array-to-dictionary/15494 "2018-09-26T00:17:37Z")\
**Posts on this page:** 17\
**Page:** 1

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**Author:** ![Rasoul](https://avatars.discourse-cdn.com/v4/letter/r/bb73d2/32.png) [@Rasoul](https://discourse.julialang.org/u/Rasoul)\
**Post date:** [September 26, 2018, 12:17am UTC](https://discourse.julialang.org/t/convert-array-to-dictionary/15494/1 "2018-09-26T00:17:37Z")

</div>

I have an array (w) including binaries (zero and one) that determines whether or not a specific action should be taken on each branch. I want to convert this array to a dictionary in which its values in w can be callable by “(f\_bus,t\_bus)”. I tried to do that by the following command

```julia
bpp= Dict( (branch["f_bus"] , branch["t_bus"]) => w[i] for (i,branch) in case["branch"])    

```

but I got the following error. Can you please guide me on doing this? Thanks in advance!

ERROR: ArgumentError: invalid index: 4

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**Author:** ![StefanKarpinski](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/stefankarpinski/32/24_2.png) [@StefanKarpinski](https://discourse.julialang.org/u/StefanKarpinski)\
**Post date:** [September 26, 2018, 1:20am UTC](https://discourse.julialang.org/t/convert-array-to-dictionary/15494/2 "2018-09-26T01:20:27Z")

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Seems likely that `4` isn’t a valid index in whatever object `w` is.

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**Author:** ![Rasoul](https://avatars.discourse-cdn.com/v4/letter/r/bb73d2/32.png) [@Rasoul](https://discourse.julialang.org/u/Rasoul)\
**Post date:** [September 26, 2018, 1:27am UTC](https://discourse.julialang.org/t/convert-array-to-dictionary/15494/3 "2018-09-26T01:27:34Z")

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w=[1;1;0;0;1;0]. I want to build a dictionary which its keys are defined by tuple (branch[“f\_bus”], branch[“t\_bus”]) and its values are w.

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**Author:** ![Elrod](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/elrod/32/22461_2.png) [@Elrod](https://discourse.julialang.org/u/Elrod)\
**Post date:** [September 26, 2018, 1:54am UTC](https://discourse.julialang.org/t/convert-array-to-dictionary/15494/4 "2018-09-26T01:54:45Z")

</div>

Please provide enough code so that we can copy and paste to reproduce.

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<div class="post-metadata">

**Author:** ![Rasoul](https://avatars.discourse-cdn.com/v4/letter/r/bb73d2/32.png) [@Rasoul](https://discourse.julialang.org/u/Rasoul)\
**Post date:** [September 26, 2018, 2:12am UTC](https://discourse.julialang.org/t/convert-array-to-dictionary/15494/5 "2018-09-26T02:12:26Z")

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bp is a tuple as follows and consists of (f-bus,t\_bus)  
(1, 2)  
(2, 3)  
(1, 4)  
(1, 5)  
(3, 4)  
(4, 5)

w is an aray equal to [1;1;0;1;0;0]. I have a line in my code (i.e., iszero(selc[bp])) which decides based on w[i] values but is callable by "bp"s. Thus I need a dictionary named “selc” in which "bp"s are keys and w[i]s are values.  
I will appreciate any help. Thanks in advance!

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<div class="post-metadata">

**Author:** ![StefanKarpinski](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/stefankarpinski/32/24_2.png) [@StefanKarpinski](https://discourse.julialang.org/u/StefanKarpinski)\
**Post date:** [September 26, 2018, 2:21am UTC](https://discourse.julialang.org/t/convert-array-to-dictionary/15494/6 "2018-09-26T02:21:08Z")

</div>

To get help, you’ll need to provide a self-contained working example.

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<div class="post-metadata">

**Author:** ![y4lu](https://avatars.discourse-cdn.com/v4/letter/y/47e85d/32.png) [@y4lu](https://discourse.julialang.org/u/y4lu)\
**Post date:** [September 26, 2018, 3:10am UTC](https://discourse.julialang.org/t/convert-array-to-dictionary/15494/7 "2018-09-26T03:10:52Z")

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I think its missing a set of square brackets for the comprehension  
`Dict([((i,i), i) for i in 1:10])`  
Add- except it does work without  
`Dict( (i,i) => i for i in 1:10)` is also ok

possibly the (i,j) iterator

```julia
[print(" $i $j ") for (i,j) in 10:-1:1]
Boundserror: Attempt to access 10 at index [2]

[print(" $i $j ") for (i,j) in zip(1:10, 10:-1:1)]
1 10 2 9 ..

```

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**Author:** ![Tamas\_Papp](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/tamas_papp/32/25949_2.png) [@Tamas\_Papp](https://discourse.julialang.org/u/Tamas_Papp)\
**Post date:** [September 26, 2018, 11:45am UTC](https://discourse.julialang.org/t/convert-array-to-dictionary/15494/8 "2018-09-26T11:45:07Z")

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quote your code, provide an MWE

> [@Please read: make it easier to help you](https://discourse.julialang.org/t/psa-make-it-easier-to-help-you/14757):
>
> Welcome to the Julia Discourse! We are enthusiastic about helping Julia programmers, both beginner and experienced. This public service announcement (PSA) outlines best practices when asking for help. Following these points makes it easier for us to help you and more likely you’ll get a prompt, useful answer. Keywords are highlighted to make it easier to refer to specific points. Choose a descriptive title that captures the key part of your question, eg “plots with multiple axes” instead of …

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<div class="post-metadata">

**Author:** ![Rasoul](https://avatars.discourse-cdn.com/v4/letter/r/bb73d2/32.png) [@Rasoul](https://discourse.julialang.org/u/Rasoul)\
**Post date:** [September 26, 2018, 1:11pm UTC](https://discourse.julialang.org/t/convert-array-to-dictionary/15494/9 "2018-09-26T13:11:22Z")

</div>

Thanks for the response! Following is piece of the code that I was intended to run. I wan to “voltage\_angle\_difference\_tighten\_index” be callable by "bp"s. I will appreciate any help!

```julia
using PowerModels
using Ipopt
using JuMP

cd("C:\\Users\\username\\.julia\\v0.6\\PowerModels\\test\\data\\matpower")
case=PowerModels.parse_file("case5.m")
pm = build_generic_model(case, QCWRTriPowerModel, PowerModels.post_opf)
result = solve_generic_model(pm, IpoptSolver())
data=case
PowerModels.update_data(data, result["solution"])

aa = getvalue(var(pm, :td))
bpp= Dict( (parse(Int,i), branch["f_bus"] , branch["t_bus"]) => aa[(branch["f_bus"],branch["t_bus"])] for (i,branch) in data["branch"])
a1 = [(k,v) for (k,v) in bpp]
angdiff1 = [y[i] for y in a1, i=2]
bus_va = Dict( parse(Int,i) => bus["va"] for (i,bus) in data["bus"])
branch_vad = Dict( (parse(Int,i), branch["f_bus"] , branch["t_bus"]) => bus_va[branch["f_bus"]] - bus_va[branch["t_bus"]] for (i,branch) in data["branch"])
a2 = [(k,v) for (k,v) in branch_vad]
angdiff2 = [z[i] for z in a2, i=2]
angdiff=floor.(10^4*(angdiff2-angdiff1))/10.0^4
b2 = [z[i] for z in a2, i=1]
c2 = [z[i] for z in b2, i=1]
voltage_angle_difference_tighten = hcat(c2,abs.(angdiff))
voltage_angle_difference_tighten_sort = sortrows(voltage_angle_difference_tighten, by=x->-x[2])
number_of_tightened_incidents=ceil(length(data["branch"])*.2)# voltage_angle_different_tightened_threshold)
sorted_branches=voltage_angle_difference_tighten_sort[:,1]
voltage_angle_difference_tighten_selected = sorted_branches[1:trunc(Int,number_of_tightened_incidents)]
voltage_angle_difference_tighten_index = zeros(length(data["branch"]),1)
voltage_angle_difference_tighten_index[trunc.(Int,voltage_angle_difference_tighten_selected)]=1

(iszero(voltage_angle_difference_tighten_index[bp])) && (continue)

```

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<div class="post-metadata">

**Author:** ![nilshg](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/nilshg/32/2283_2.png) [@nilshg](https://discourse.julialang.org/u/nilshg)\
**Post date:** [September 26, 2018, 2:04pm UTC](https://discourse.julialang.org/t/convert-array-to-dictionary/15494/10 "2018-09-26T14:04:28Z")

</div>

Thanks for posting this, but I think what Stefan and Tamas were looking for is slightly different - the key aspects of an MWE are that it is both **M** inimal and **W** orking.

From the code snippet you posted it appears unlikely that it is minimal (there seem to be a lot of rows unrelated to dictionary operations), and it also seems unlikely that it is working (given that it accesses a local file on your computer to construct the `case` variable).

It’d be really helpful if you could try to narrow your problem down to a small number of lines sufficient to produce the error you’re running into.

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<div class="post-metadata">

**Author:** ![Rasoul](https://avatars.discourse-cdn.com/v4/letter/r/bb73d2/32.png) [@Rasoul](https://discourse.julialang.org/u/Rasoul)\
**Post date:** [September 26, 2018, 2:35pm UTC](https://discourse.julialang.org/t/convert-array-to-dictionary/15494/11 "2018-09-26T14:35:28Z")

</div>

Thanks for the response!  
I narrow the code down to a small number of lines. The line in for loop produce the error because it is not callable with “bp”. “voltage\_angle\_difference\_tighten\_index” needs to be converted to a dictionary which can be callable by "bp"s. I will appreciate any help!

```julia
using PowerModels
using Ipopt
using JuMP

cd("C:\\Users\\username\\.julia\\v0.6\\PowerModels\\test\\data\\matpower")
case=PowerModels.parse_file("case5.m")
pm = build_generic_model(case, QCWRTriPowerModel, PowerModels.post_opf)
result = solve_generic_model(pm, IpoptSolver())
data=case
PowerModels.update_data(data, result["solution"])

voltage_angle_difference_tighten_index=[1;1;0;0;1;0];
for bp in buspairs
(iszero(voltage_angle_difference_tighten_index[bp])) && (continue)
end

```

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<div class="post-metadata">

**Author:** ![tamasgal](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/tamasgal/32/27946_2.png) [@tamasgal](https://discourse.julialang.org/u/tamasgal)\
**Post date:** [September 26, 2018, 3:04pm UTC](https://discourse.julialang.org/t/convert-array-to-dictionary/15494/12 "2018-09-26T15:04:43Z")

</div>

A code which contains lines like this:

> [@Rasoul](#):
>
> cd(“C:\Users\username\.julia\v0.6\PowerModels\test\data\matpower”) case=PowerModels.parse\_file(“case5.m”)

will likely not run on any of our machines 😉 I hope you agree…

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<div class="post-metadata">

**Author:** ![nilshg](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/nilshg/32/2283_2.png) [@nilshg](https://discourse.julialang.org/u/nilshg)\
**Post date:** [September 26, 2018, 3:04pm UTC](https://discourse.julialang.org/t/convert-array-to-dictionary/15494/13 "2018-09-26T15:04:55Z")

</div>

Thanks for improving your code snippet, but I don’t think we’re quite there yet:

1. It still appears this isn’t a **M** inimal example - the dependencies on `PowerModels`, `Ipopt`, `JuMP` seem unnecessary;
2. It also isn’t **W** orking - I assume the key bit we’re interested in is the last loop, however `buspairs` is undefined so this doesn’t run.

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<div class="post-metadata">

**Author:** ![Rasoul](https://avatars.discourse-cdn.com/v4/letter/r/bb73d2/32.png) [@Rasoul](https://discourse.julialang.org/u/Rasoul)\
**Post date:** [September 26, 2018, 3:15pm UTC](https://discourse.julialang.org/t/convert-array-to-dictionary/15494/14 "2018-09-26T15:15:58Z")

</div>

> [@nilshg](#):
>
> snippet

buspairs definition is in PowerModels.jl and that is why I put using PowerModels. the code needs the PowerModels package to be added. After adding the package my code snippet would work.

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<div class="post-metadata">

**Author:** ![nilshg](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/nilshg/32/2283_2.png) [@nilshg](https://discourse.julialang.org/u/nilshg)\
**Post date:** [September 26, 2018, 3:33pm UTC](https://discourse.julialang.org/t/convert-array-to-dictionary/15494/15 "2018-09-26T15:33:18Z")

</div>

Apologies, that wasn’t clear to me - although I get (on v0.7, having added `PowerModels`):

```julia
julia> using PowerModels

julia> buspairs
UndefVarError: buspairs not defined

```

However it seems your question only relates to indexing dictionaries and standard Arrays, so again it seems unlikely that `PowerModels` is required to demonstrate your problem.

If your problem is related to `voltage_angle_difference_tighten_index[bp]` in the loop, ideally you could just create a `buspair` object using dummy data?

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<div class="post-metadata">

**Author:** ![Rasoul](https://avatars.discourse-cdn.com/v4/letter/r/bb73d2/32.png) [@Rasoul](https://discourse.julialang.org/u/Rasoul)\
**Post date:** [September 26, 2018, 3:44pm UTC](https://discourse.julialang.org/t/convert-array-to-dictionary/15494/16 "2018-09-26T15:44:22Z")

</div>

Thanks for the response! Following is exactly what I asked yesterday.  
bp is a tuple as follows  
(1, 2)  
(2, 3)  
(1, 4)  
(1, 5)  
(3, 4)  
(4, 5)

w is an aray equal to [1;1;0;1;0;0]. I have a line in my code (i.e., iszero(selc[bp])) which decides based on w[i] values but is callable by "bp"s. Thus I need a dictionary named “selc” in which "bp"s are keys and w[i]s are values.

---

<div class="post-metadata">

**Author:** ![nilshg](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/nilshg/32/2283_2.png) [@nilshg](https://discourse.julialang.org/u/nilshg)\
**Post date:** [September 26, 2018, 3:53pm UTC](https://discourse.julialang.org/t/convert-array-to-dictionary/15494/17 "2018-09-26T15:53:21Z")

</div>

Okay, this is a lot closer to an MWE, although I’m still not sure what you’re trying to achieve.

Here’s an MWE of what I currently think you’re trying to do:

```julia
w=[1;1;0;0;1;0]
buspairs = [(1, 2) (2, 3) (1, 4) (1, 5) (3, 4) (4, 5)]

d = Dict(buspairs[i] => w[i] for i ∈ 1:6)

d[(1,4)] # returns 0

```