remove numbers of an matrix from another matrix

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Alberto Acri il 18 Set 2023
Commentato: Alberto Acri il 18 Set 2023
Hi. How can I remove numbers of an matrix from another matrix?
I have two matrices:
M1 = [7 21; 41 52; 47 65; 14 41; 14 55];
M11 = [14 55; 47 65; 41 52; 14 41; 7 21];
M2 = [5 15; 7 21; 41 52; 47 65; 98 74; 14 41; 36 54; 36 47; 14 55; 14 88];
• I need to check if M1 (or M11) is contained in M2.
• I need to remove the values of M1 (or M11) from M2 with this end result:
M3 = [5 15; 98 74; 36 54; 36 47; 14 88];
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Harry il 18 Set 2023
To clarify, are you wanting to remove the rows of M2 if the entire row is replicated in either M1 or M11, or remove the row if only one number is repeated?
For example, if the you had:
M1 = [7 22; 41 52]
Would the [7 21] row need removing from M2 or not?
Alberto Acri il 18 Set 2023
Good observation. If the row of M1 (or M11) is present in M2!

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Risposta accettata

Dyuman Joshi il 18 Set 2023
Modificato: Dyuman Joshi il 18 Set 2023
M1 = [7 21; 41 52; 47 65; 14 41; 14 55];
M11 = [14 55; 47 65; 41 52; 14 41; 7 21];
M2 = [5 15; 7 21; 41 52; 47 65; 98 74; 14 41; 36 54; 36 47; 14 55; 14 88];
%Checking which rows in M2 are common with M1
[idx1,idx2] = ismember(M2,M1,'rows')
idx1 = 10×1 logical array
0 1 1 1 0 1 0 0 1 0
idx2 = 10×1
0 1 2 3 0 4 0 0 5 0
idx1 shows whether a row in M2 is present in M1 or not.
idx2 shows the corresponding indices of rows of M1 if present, 0 if not -
The 1st row in M2 is not common with in M1, The 2nd row in M2 is common with 1st row in M1, and so on.
%Removing the common rows
M2(idx1,:) = []
M2 = 5×2
5 15 98 74 36 54 36 47 14 88
%or
%Retaining the uncommon rows
%M2=M2(~idx1,:);
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Steven Lord il 18 Set 2023
Call setdiff with the 'rows' input.
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