I have some data in 10 matrices. Each matrix has a different number of rows, but the same number of columns.
I want to combine all 10 matrices to one matrix row-wise, interleaved, meaning the rows in that matrix will look like:
row 1 from matrix 0
...
row 1 from matrix 9
row 2 from matrix 0
...
row 2 from matrix 9
...
Example (with 3 matrices):
Matrix 1: [1 2 3 ; 4 5 6; 7 8 9]
Matrix 2: [3 2 1 ; 6 5 4]
Matrix 3: [1 1 1 ; 2 2 2 ; 3 3 3]
Combined matrix will be: [1 2 3 ; 3 2 1 ; 1 1 1 ; 4 5 6 ; 6 5 4 ; 2 2 2 ; 7 8 9 ; 3 3 3]
You can download the function interleave2 here https://au.mathworks.com/matlabcentral/fileexchange/45757-interleave-vectors-or-matrices
z = interleave2(a,b,c,'row')
you can see the way the function works in the source code of course
Here's a general solution that allows you to place however many matrices you want (with matching number of columns) into the starting cell array Result:
Result = {Matrix1, Matrix2, Matrix3};
index = cellfun(#(m) {1:size(m, 1)}, Result);
[~, index] = sort([index{:}]);
Result = vertcat(Result{:});
Result = Result(index, :);
This will generate an index vector 1:m for each matrix, where m is its number of rows. By concatenating these indices and sorting them, we can get a new index that can be used to sort the rows of the vertically-concatenated set of matrices so that they are interleaved.
Related
I have 2 matrices (D:76572x2 and E:1850092x7) and want the values of rows in the larger matrix (E) if the the first two columns are equal to any row of the smaller matrix (D).
Example:
D = [1000 19751231;
1000 19761231]
E = [1234 19701130 4 5 2 9 3;
1000 19751231 2 3 2 5 2]
So in that case I only want the row: [1000 19751231 2 3 2 5 2] from matrix E. How can I compute this relatively quickly for a large matrix without using any/many (for-)loops?
Thanks
We can use the ismember function here
rows_E = ismember(E(:,1:2),D,'rows');
From your example:
>> E(rows_E,:)
Yields
ans =
1000 19751231 2 3 2 5 2
I have a series of numbers:
test = [1 1 1 2 2 2 3 3 3 4 4 4 5 5 5]
which I want to randomely fill into a 3x5 matrix without having the same number in the same row.
How can I do this in matlab? Potentially I could randomize the test vector and fill it into the 5x3 matrix but I don't know how to do this without getting the same number in the same row.
If you want to fill a 3-by-5 matrix with all of the values in test, making sure each row has no repeated values, you can do this very succinctly by using toeplitz to first generate an index matrix, then randomly permute the dimensions with randperm:
index = toeplitz(1:3, [3 5:-1:2]);
index = index(randperm(3), randperm(5));
And a sample index:
index =
1 5 4 2 3
4 3 2 5 1
5 4 3 1 2
If your values in test are the numbers 1 through 5, this should be all you need to do. If test could be any vector with with 5 different numbers, three of each, then you can get the unique values of your test vector and index them with index. This solution will generalize to any test vector:
test = [3 3 3 7 7 7 5 5 5 9 9 9 4 4 4]; % Sample data
uniqueValues = unique(test); % Get the unique values [3 4 5 7 9]
M = uniqueValues(index); % Use index as generated above
And the result will be guaranteed to be a reordered version of what's in test:
M =
3 9 7 4 5
7 5 4 9 3
9 7 5 3 4
You can take the unique matrix of test and pick any three elements out of it and fill in the required 5X3 matrix.
test = [1 1 1 2 2 2 3 3 3 4 4 4 5 5 5] ;
test_unique = unique(test) ;
A = zeros(5,3) ;
for i = 1:size(A,1)
A(i,:) = randsample(test_unique,3) ;
end
randsample needs a statistics toolbox, if you doesn't have it, you may use randperm as shown below.
test = [1 1 1 2 2 2 3 3 3 4 4 4 5 5 5] ;
test_unique = unique(test) ;
A = zeros(5,3) ;
for i = 1:size(A,1)
A(i,:) = test_unique(randperm(length(test_unique),3)) ;
end
If you want 3X5 matrix:
test = [1 1 1 2 2 2 3 3 3 4 4 4 5 5 5] ;
test_unique = unique(test) ;
A = zeros(3,5) ;
for i = 1:size(A,1)
A(i,:) = randsample(test_unique,5) ;
end
Here is a brute-force way of doing it
% data
test = [1 1 1 2 2 2 3 3 3 4 4 4 5 5 5];
% randomly permute the indices
indices = randperm(numel(test));
% create a random matrix
matrix = reshape(test(indices), 5, 3);
% while number of unique elements in any of the rows is other than 3
while any(arrayfun(#(x) numel(unique(matrix(x,:))), (1:size(matrix,1)).')~=3)
% keep generating random matrices
indices = randperm(numel(test));
matrix = reshape(test(indices), 5, 3);
end;
% here is the result
result=matrix;
EDIT : If you want 3x5 like you mentioned in your comment, it is a lot easier. Just one line below.
[~, result] = sort(rand(3,5),2);
I have a Matrix of size M by N in which each row has some zero entries. I want to create M row vectors such that each of the vector contains the non zero elements of each row. For example if I have the following Matrix
A=[0 0 0 5;0 0 4 6;0 1 2 3;9 10 2 3]
I want four different row vectors of the following form
[5]
[4 6]
[1 2 3]
[9 10 2 3]
This can be done with accumarray using an anonymous function as fourth input argument. To make sure that the results are in the same order as in A, the grouping values used as first input should be sorted. This requires using (a linearized version of) A transposed as second input.
ind = repmat((1:size(A,2)).',1,size(A,2)).';
B = A.';
result = accumarray(ind(:), B(:), [], #(x){nonzeros(x).'});
With A = [0 0 0 5; 0 0 4 6; 0 1 2 3; 9 10 2 3]; this gives
result{1} =
5
result{2} =
4 6
result{3} =
1 2 3
result{4} =
9 10 2 3
Since Matlab doesn't support non-rectangular double arrays, you'll want to settle on a cell array. One quick way to get the desired output is to combine arrayfun with logical indexing:
nonZeroVectors = arrayfun(#(k) A(k,A(k,:)~=0),1:size(A,1),'UniformOutput',false);
I used the ('UniformOutput',false) name-value pair for the reasons indicated in the documentation (I'll note that the pair ('uni',0) also works, but I prefer verbosity). This input produces a cell array with the entries
>> nonZerosVectors{:}
ans =
5
ans =
4 6
ans =
1 2 3
ans =
9 10 2 3
In Matlab I have a big matrix containing the coordinates (x,y,z) of many points (over 200000). There is an extra column used as identification. I have written this code in order to sort all coordinate points. My final goal is to find duplicated points (rows with same x,y,z). After sorting the coordinate points I use the diff function, two consecutive rows of the matrix with the same coordinates will take value [0 0 0], and then with ismember I can find which rows of that matrix resulting from applying "diff" have the [0 0 0] row. With the indices returned from ismember I can find which points are repeated.
Back to my question...This is the code I wrote to sort properly my coordintes+id matrix. I guess It could be done better. Any suggestion?
%coordinates are always positive
a=[ 1 2 8 4; %sample matrix
1 0 5 6;
2 4 7 1;
3 2 1 0;
2 3 5 0;
3 1 2 8;
1 2 4 8];
b=a; %for checking purposes
%sorting first column
a=sortrows(a,1);
%sorting second column
for i=0:max(a(:,1));
k=find(a(:,1)==i);
if not(isempty(k))
a(k,:)=sortrows(a(k,:),2);
end
end
%Sorting third column
for i=0:max(a(:,2));
k=find(a(:,2)==i);
if not(isempty(k))
%identifying rows with same value on first column
for j=1:length(k)
[rows,~] = ismember(a(:,1:2), [ a(k(j),1),i],'rows');
a(rows,3:end)=sortrows(a(rows,3:end),1);
end
end
end
%Checking that rows remain the same
m=ismember(b,a,'rows');
if length(m)~=sum(m)
disp('Error while sorting!');
end
Why don't you just use unique?
[uniqueRows, ii, jj] = unique(a(:,1:3),'rows');
Example
a = [1 2 3 5
3 2 3 6
1 2 3 9
2 2 2 8];
gives
uniqueRows =
1 2 3
2 2 2
3 2 3
and
jj =
1
3
1
2
meaning third row equals first row.
If you need the full unique rows, including the fourth column: use ii to index a:
fullUniqueRows = a(ii,:);
which gives
fullUniqueRows =
1 2 3 9
2 2 2 8
3 2 3 6
Trying to sort a based on the fourth column? Do this -
a=[ 1 2 8 4; %sample matrix
1 0 5 6;
2 4 7 1;
3 2 1 0;
2 3 5 0;
3 2 1 8;
1 2 4 8];
[x,y] = sort(a(:,4))
sorted_a=a(y,:)
Trying to get the row indices having repeated x-y-z coordinates being represented by the first three columns? Do this -
out = sum(squeeze(all(bsxfun(#eq,a(:,1:3),permute(a(:,1:3),[3 2 1])),2)),2)>1
and use it similarly for sorted_a.
I am trying to get the sort of row and column according to the value of matrix.
for example, if the matrix is
A = [3 4 7; 9 8 6; 2 1 5]
it should output
2 1
2 2
1 3
2 3
3 3
1 2
1 1
3 1
3 2
I think that should be simple, but I do not have an idea about how to handle that.
Yes it is indeed very simple.
%sort the vector instead of matrix to get linear indices
[~,ind]=sort(A(:),'descend')
%convert the linear indices to [row,col] subscripts
[I,J]=ind2sub(size(A),ind)
%display desired answer
[I J]
To delete rows which have same value in both the columns:
A(A(:,1)==A(:,2),:)=[]