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Find the difference between all columns of a given row of a matrix

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I have MXL matrix. For each row, I want to find the absolute difference between the columns, without repeating. For example, if I have a row
a = [a11 a12 a13 a14]
I want to find
[abs(a11-a12) abs(a11-a13) abs(a11-a14) abs(a12-a13) abs(a12-a14) abs(a13-a14)]
How can I do that withoug for loops?
EDIT: I found this method
pdist([2 3 1 4]',@(x,y) x-y)
which looks like what I'm looking for, but I need to extend this for a matrix, and perform the above for all rows.

Akzeptierte Antwort

Antoni Garcia-Herreros
Antoni Garcia-Herreros am 8 Mai 2023
Hello MAWE,
You could use the function nchoosek:
Something like this might work for your case:
A=rand(4,5); % Generate data for the example
perms = nchoosek(1:size(A,2),2); % Find all the possible permutations
D=abs(A(:,perms(:,2))-A(:,perms(:,1))) % Compute the difference
D = 4×10
0.1875 0.5928 0.3519 0.1090 0.4053 0.1644 0.0785 0.2409 0.4838 0.2429 0.3220 0.2441 0.1334 0.3684 0.0779 0.4555 0.6904 0.3775 0.6125 0.2350 0.4037 0.4237 0.0883 0.1470 0.8274 0.3155 0.2568 0.5120 0.5707 0.0587 0.5416 0.0068 0.6400 0.3387 0.5348 0.0984 0.2029 0.6332 0.3319 0.3013
Hope this helps

Weitere Antworten (1)

Luca Ferro
Luca Ferro am 8 Mai 2023
Bearbeitet: Luca Ferro am 8 Mai 2023
a=[1 3 5 -3];
aPerms=nchoosek(a,2); %generates all unique couples
absDiff=abs(aPerms(:,1)-aPerms(:,2))' %absolute difference of said couples, ' to transpose
absDiff = 1×6
2 4 4 2 6 8

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