Find the rows of a matrix with conditions concerning the values of certain columns in matlab

问题

As the title says, I want to find all rows in a Matlab matrix that in certain columns the values in the row are equal with the values in the previous row, or in general, equal in some row in the matrix. For example I have a matrix

and I want to find the following rows:

1 2 3 4 
1 2 3 10
1 2 4 7

How do I do something like that and how do I do it generally for all the possible pairs in columns 1 and 2, and have equal values in previous rows, that exist in the matrix?

回答1:

Here's a start to see if we're headed in the right direction:

>> M = [1 2 3 4;
     1 2 8 10;
     4 5 7 9;
     2 3 6 4;
     1 2 4 7];

>> N = M;  %// copy M into a new matrix so we can modify it
>> idx = ismember(N(:,1:2), N(1,1:2), 'rows')

idx =

   1
   1
   0
   0
   1

>> N(idx, :)
ans =

    1    2    3    4
    1    2    8   10
    1    2    4    7

Then you can remove those rows from the original matrix and repeat.

>> N = N(~idx,:)
N =

   4   5   7   9
   2   3   6   4

回答2:

this will give you the results

data1 =[1 2 3 4
1 2 8 10
4 5 7 9
2 3 6 4
1 2 4 7];

data2 = [1 2 3 4 
1 2 3 10
1 2 4 7];

[exists,position] = ismember(data1,data2, 'rows')

where the exists vector tells you wheter the row is on the other matrix and position gives you the position...

a less elegant and simpler version would be

array_data1 = reshape (data1',[],1);
array_data2 = reshape (data2',[],1);

matchmatrix = zeros(size(data2,1),size(data1,1));
for irow1 = 1: size(data2,1)
    for irow2 = 1: size(data1,1)
        matchmatrix(irow1,irow2) = min(data2(irow1,:) == data1(irow2,:))~= 0;
    end
end

the matchmatrix is to read as a connectivity matrix where value of 1 indicates which row of data1 matches with which row of data2

来源：https://stackoverflow.com/questions/33316919/find-the-rows-of-a-matrix-with-conditions-concerning-the-values-of-certain-colum

标签

matlab

find

rows