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join tables by categorical variable

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cl
cl on 13 Jul 2020
Commented: Peter Perkins on 24 Jul 2020
I want to join two tables with indices of type categorical. However, I get an error.
I can convert both indices to string, then join, and then convert back to categorical again, but that seems ludicrous.
a = table(categorical(["a", "b", "c"]'), [1:3]')
b = table(categorical(["a", "b", "d"]'), [4:6]')
join(a,b,'Keys','Var1')
Gives "Left and right key variables 'Var1' and 'Var1' have incompatible types."

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Accepted Answer

cl
cl on 24 Jul 2020
Turns out that my Matlab installation was corrupted, causing the mis-leading error message I received. After re-installation the error message changed and with using innerjoin instead of join on Akira's suggestion the code executed without errors. Thanks.

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More Answers (1)

Akira Agata
Akira Agata on 14 Jul 2020
Please try innerjoin or outerjoin functions, like:
c1 = innerjoin(a,b,'Keys','Var1');
c2 = outerjoin(a,b,'Keys','Var1','MergeKeys',true);
These outputs are as follows:
>> c1
c1 =
2×3 table
Var1 Var2_a Var2_b
____ ______ ______
a 1 4
b 2 5
>> c2
c2 =
4×3 table
Var1 Var2_a Var2_b
____ ______ ______
a 1 4
b 2 5
c 3 NaN
d NaN 6

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Akira Agata
Akira Agata on 20 Jul 2020
Thank you for the clarification. I've confirmed that the above code works at least in my R2019b environment (more specifically, R2019b Update 3 on Windows 10).
Thus, it might be related to your specific running environment (OS, MATLAB and/or Update version, etc). So, at this stage, I would recommend contacting our Technical Support team.
Steven Lord
Steven Lord on 20 Jul 2020
The problem, I believe, is that the categorical array used for Var1 in a does not have the same categories as the categorical array used for Var1 in b.
categories(a.Var1)
categories(b.Var1)
If you had two categorical arrays, one listing pieces of a house (door, window, chimney) and one listing pieces of a car (door, window, motor) those are both categorical arrays but they're different because each has a category the other doesn't (chimney, motor.)
Peter Perkins
Peter Perkins on 24 Jul 2020
As long as the categoricals are not ordinal, the different categories should not matter. If they are ordinal, the categories must be the same, with the same order.
But in any case, the OP says, "Turns out that my Matlab installation was corrupted, causing the mis-leading error message I received."

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