Get all unique combinations of 2 columns from a table

Question

Austin Burritt 2022-1-19

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https://ww2.mathworks.cn/matlabcentral/answers/1631910-get-all-unique-combinations-of-2-columns-from-a-table

评论： Austin Burritt 2022-1-19

I have a table that has 4 variables, similar to this:

    Item1    Item2    Item3    Item4
    _____    _____    _____    _____
      1        5        7       10  
      

What is the best way to produce the delta of each combination of columns? Ex. Item1 vs Item2, Item1 vs Item3, etc.

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Answer 1

Stephen23 2022-1-19

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在 MATLAB Online 中打开

V = {'Item1','Item2','Item3','Item4'};
T = table(1, 5, 7 ,10, 'VariableNames',V)
T = 1×4 table
    Item1    Item2    Item3    Item4
    _____    _____    _____    _____

      1        5        7       10  
X = nchoosek(1:numel(V),2);
D = diff(T{:,V}(X),1,2);
Z = cell2table([V(X),num2cell(D)])
Z = 6×3 table
      Var1         Var2       Var3
    _________    _________    ____

    {'Item1'}    {'Item2'}     4  
    {'Item1'}    {'Item3'}     6  
    {'Item1'}    {'Item4'}     9  
    {'Item2'}    {'Item3'}     2  
    {'Item2'}    {'Item4'}     5  
    {'Item3'}    {'Item4'}     3  

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Answer 2

Cris LaPierre 2022-1-19

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https://ww2.mathworks.cn/matlabcentral/answers/1631910-get-all-unique-combinations-of-2-columns-from-a-table#answer_877440

I would look into using the perms function, along with the unique and diff functions.

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Cris LaPierre 2022-1-19

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I was probably trying too hard to make use of the variablenames. Stephen's approach is simpler by using column numbers instead.

T = table(1, 5, 7 ,10, 'VariableNames', {'Item1' 'Item2' 'Item3' 'Item4'});
C = nchoosek(T.Properties.VariableNames,2)
C = 6×2 cell array
    {'Item1'}    {'Item2'}
    {'Item1'}    {'Item3'}
    {'Item1'}    {'Item4'}
    {'Item2'}    {'Item3'}
    {'Item2'}    {'Item4'}
    {'Item3'}    {'Item4'}
delta = diff([T{1,{C{:,1}}};T{1,{C{:,2}}}])
delta = 1×6
     4     6     9     2     5     3