# Comparing Unequal Dictionaries
**URL:** https://discourse.julialang.org/t/comparing-unequal-dictionaries/52048
**Category:** New to Julia
**Created:** [December 18, 2020, 2:35pm UTC](https://discourse.julialang.org/t/comparing-unequal-dictionaries/52048 "2020-12-18T14:35:00Z")
**Posts on this page:** 8
**Page:** 1
### Author:  [@SergeantMike67](https://discourse.julialang.org/u/SergeantMike67)
#### Post date: [December 18, 2020, 2:35pm UTC](https://discourse.julialang.org/t/comparing-unequal-dictionaries/52048/1 "2020-12-18T14:35:00Z")
So after reading about everything I can find on the subject, I am going to throw in the towel and ask.
I have 2 dictionaries “a” and “b”
a = 4-element Array{Pair{Union{Missing, Int16},Int64},1}:
133 =\> 2
135 =\> 9
137 =\> 1
143 =\> 4
b = 6-element Array{Pair{Union{Missing, Int16},Int64},1}:
129 =\> 10
131 =\> 9
133 =\> 8
135 =\> 14
137 =\> 2
141 =\> 1
what I want to do is get the difference between the values in each key
the code I have so far is
for (index,value) in a
for (indexj,valuej) in b
if index==indexj
difference= abs(value-valuej)
end
end
end
However, because the Dictionaries are of unequal size, I cannot get the numbers for 129 and 141 in “b” and 143 in “a” because there isn’t a match in both sets. How do I get these values included in the sum of differences?
---
### Author:  [@Rudi79](https://discourse.julialang.org/u/Rudi79)
#### Post date: [December 18, 2020, 3:10pm UTC](https://discourse.julialang.org/t/comparing-unequal-dictionaries/52048/2 "2020-12-18T15:10:09Z")
It depends on what you want. What should the difference be if one key is not present in both dicts?
Assuming a default value of 0, the result could look something like
```julia
difference = sum(values(mergewith( (x,y) -> abs(x-y), a, b)))
```
Or a bit more verbose so you can better see what is going on could be:
```julia
diff = 0
same = intersect(keys(a), keys(b))
for i in same
diff += abs(a[i]-b[i])
end
for i in setdiff(keys(a), same)
diff += a[i]
end
for i in setdiff(keys(b), same)
diff += b[i]
end
```
I would also like to suggest reading this post:
> [@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 …
---
### Author:  [@SergeantMike67](https://discourse.julialang.org/u/SergeantMike67)
#### Post date: [December 18, 2020, 3:46pm UTC](https://discourse.julialang.org/t/comparing-unequal-dictionaries/52048/3 "2020-12-18T15:46:15Z")
oops sorry, should have followed the formatting structure. Will do so in the future
When I try the one line statement, I get this error:
```julia
ERROR: MethodError: no method matching mergewith(::var"#21#22", ::Array{Pair{Union{Missing, Int16},Int64},1}, ::Array{Pair{Union{Missing, Int16},Int64},1})
Closest candidates are:
mergewith(::Any) at abstractdict.jl:350
mergewith(::Any, ::AbstractDict, ::AbstractDict...) at abstractdict.jl:348
Stacktrace:
[1] top-level scope at none:1
```
I am using V1.5.1. I am curious as to why I am getting this error
---
### Author:  [@contradict](https://discourse.julialang.org/u/contradict)
#### Post date: [December 18, 2020, 7:01pm UTC](https://discourse.julialang.org/t/comparing-unequal-dictionaries/52048/4 "2020-12-18T19:01:22Z")
Because you aren’t using dictionaries. Your `a` and `b` are
```julia
a = 4-element Array{Pair{Union{Missing, Int16},Int64},1}:
```
I’m not sure how you got there, maybe by calling `collect` on a `Dict{Union{Missing, Int16}, Int64}`? In any case, try applying `Dict()` to `a` and `b` before `mergewith`
---
### Author:  [@SergeantMike67](https://discourse.julialang.org/u/SergeantMike67)
#### Post date: [December 18, 2020, 7:49pm UTC](https://discourse.julialang.org/t/comparing-unequal-dictionaries/52048/5 "2020-12-18T19:49:05Z")
I did use a `collect` to pull out the two groups of data from a larger dataframe.
---
### Author:  [@contradict](https://discourse.julialang.org/u/contradict)
#### Post date: [December 19, 2020, 12:26am UTC](https://discourse.julialang.org/t/comparing-unequal-dictionaries/52048/6 "2020-12-19T00:26:15Z")
Oh, in that case there might be a way to do what you want while keeping things in a Dataframe. Can you show a more complete example of what you want to accomplish?
---
### Author:  [@SergeantMike67](https://discourse.julialang.org/u/SergeantMike67)
#### Post date: [December 19, 2020, 5:58pm UTC](https://discourse.julialang.org/t/comparing-unequal-dictionaries/52048/7 "2020-12-19T17:58:16Z")
What I am attempting to do is determine the sum of squares between 2 populations at one genetic loci. For example: in an organism there at locus A there are several variations on the gene. What I need to do is find the differences between the populations. So basically if there is a way to compare the populations while in the dataframe then I am all for it.
Here is some example data
```julia
153×3 DataFrame
│ Row │ locus │ population │ counts │
│ │ String │ String │ Dict{Union{Missing, Int16},Int64} │
├─────┼────────┼────────────┼───────────────────────────────────────────────────────────────────────────────────────────┤
│ 1 │A│ 1 │ Dict(133=>2,135=>9,143=>4,137=>1) │
│ 2 │A│ 2 │ Dict(133=>8,135=>14,131=>9,137=>2,129=>10,141=>1) │
│ 3 │A│ 3 │ Dict(135=>1,123=>4,145=>2,143=>1,137=>10,139=>1,141=>5) │
│ 4 │A| 4 │ Dict(133=>1,135=>7,147=>2,123=>3,145=>3,143=>1,137=>17,149=>1,139=>3,141=>8) │
│ 5 │A│ 5 │ Dict(135=>7,147=>1,123=>1,145=>2,143=>6,137=>10,139=>1,141=>2) │
│ 6 │A│ 6 │ Dict(135=>2,121=>1,123=>3,145=>1,137=>4,139=>9,141=>2) │
│ 7 │A│ 7 │ Dict(133=>3,135=>7,123=>2,137=>2,149=>2,141=>2) │
│ 8 │A│ 8 │ Dict(133=>1,135=>9,123=>1,143=>1,137=>7,141=>1) │
│ 9 │A| 9 │ Dict(135=>8,121=>3,123=>1,137=>6) │
│ 10 │A│ 10 │ Dict(135=>10,123=>2,143=>9,139=>1) │
```
Where` locus string` is the locus name, `population string` is the population number(may or may not be numeric that depends on what the researcher entered here and `counts` are the number of individuals that have that version of the gene in that population. The versions do not have to have numeric names they can be alphanumeric.
example: Population 1 at locus A; 2 individuals have version 133, 9 individuals have version 135, 4 individuals have version 143, and 1 individual has version 137
---
### Author:  [@contradict](https://discourse.julialang.org/u/contradict)
#### Post date: [December 19, 2020, 10:29pm UTC](https://discourse.julialang.org/t/comparing-unequal-dictionaries/52048/8 "2020-12-19T22:29:52Z")
OK, I think I was wrong, I don’t see a nice way to fit that into a dataframe. Your collect was probably on the right track. How about constructing a matrix of all pairwise comparisons?
```julia
compare(a, b) = sum(values(mergewith( (x,y) -> abs(x-y), a, b)))
counts = df.counts
differences = compare.(permutedims(counts), counts)
```