I have two cells of strings: A(a,1) and B(b,1), where a>b.
I want to combine A with B, adding B at a certain position of A.
Notice that in A there are no blank rows, so I suppose that first I have to add b blank rows in A and then concatenate B at a specific position.
Any suggestion?
Thank you :)
Suppose that you want to place B in the position p of A. You can use indexing and concatenation of cell arrays like any other array types:
A = [A(1:p - 1, 1); B; A(p:end, 1)];
Related
Say A is a 3x4x5 array. I am given a vector a, say of dimension 2 and b of dimension 2. If I do A(a,b,:) it will give 5 matrices of dimensions 2x2. I instead want the piecewise vectors (without writing a for loop).
So, I want the two vectors of A which are given by (a's first element and b's first element) and (a's second element and b's second element)
How do I do this without a for loop? If A were two dimensions I could do this using sub2ind. I don't know how to access the entire vectors.
You can use sub2ind to find the linear index to the first element of each output vector: ind = sub2ind(size(A),a,b). To get the whole vectors, you can't do A(ind,:), because the : has to be the 3rd dimension. However, what you can do is reshape A to be 2D, collapsing the first two dimensions into one. We have a linear index to the vectors we want, that will correctly index the first dimension of this reshaped A:
% input:
A = rand(3,4,5);
a = [2,3];
b = [1,2];
% expected:
B = [squeeze(A(a(1),b(1),:)).';squeeze(A(a(2),b(2),:)).']
% solution:
ind = sub2ind(size(A),a,b);
C = reshape(A,[],size(A,3));
C = C(ind,:)
assert(isequal(B,C))
You can change a and b to be 3d arrays just like A and then the sub2ind should be able to index the whole matrix. Like this:
Edit: Someone pointed out a bug. I have changed it so that a correction gets added. The problem was that ind1, which should have had the index number for each desired element of A was only indexing the first "plane" of A. The fix is that for each additional "plane" in the z direction, the total number of elements in A in the previous "planes" must be added to the index.
A=rand(3,4,5);
a=[2,3];
b=[1,2];
a=repmat(a,1,1,size(A,3));
b=repmat(b,1,1,size(A,3));
ind1=sub2ind(size(A),a,b);
correction=(size(A,1)*size(A,2))*(0:size(A,3)-1);
correction=permute(correction,[3 1 2]);
ind1=ind1+repmat(correction,1,2,1);
out=A(ind1)
I have a cell array (A) with size of 400 x 1 and each cell of this array includes a matrix with size 9 x 4. As such, it looks like this:
A={[9x4 double];[9x4 double];...;[9x4 double]};
Now, I want to remove the zero rows from these sub matrices and then obtain a new A cell array called A_new where its sub matrices don't have any zero rows like this:
A_new={[5x4 double];[7x4 double];...;[4x4 double]};
By my below code, I can find the index of rows which are not zero but I couldn't create my cell array like I mentioned above. This is my written code and for the bold part, I have a problem and I couldn't solve it.
for i=1:A_Length
[row,col]=find(A{i,1});
out=[row col];
NNZ_row=unique(row);
Length_NNZ= length(NNZ_row);
for j=1:Length_NNZ
**A_NonZero{i,1}= ??????????**
end
end
What I would do is take each cell, then use all on the opposite of the matrix over all of the columns in each row to determine which rows contain all zeroes. Once you do this, use these locations and remove those rows from this matrix and save this to your new matrix.
As such, do this:
A_new = cell(1,numel(A));
for i=1:numel(A)
mat = A{i};
ind = all(~mat, 2);
A_new{i} = mat(~ind,:);
end
The first line of code creates a new cell array that is the same size as A. Next, for each element in A, extract the matrix at each cell location, use all on the opposite of this matrix to find those elements that we need to keep, then save this new matrix into the corresponding location in A_new.
If you want to do this in a single line of code, use cellfun:
A_new = cellfun(#(x) x(~all(~x,2),:), A, 'uni', 0);
The first argument to cellfun is an anonymous function that performs what the for loop was doing. We find those rows that contain all zeroes and use those to remove the rows in each matrix in the cell array. The second argument is the matrix we want to operate on, which is A. The 'uni' and 0 flags are important because the outputs are not single values but matrices, and so the output of this function will be a cell array that is the same size as A where each element is the matrix for those corresponding locations in A with the zero rows removed.
You should use a combination of cellfun and any:
A_new = cellfun(#(x) x(any(x~=0,2),:), A, 'UniformOutput', false);
should do the trick.
Going nuts with cell array, because I just can't get rid of it... However, it will be an easy one for you guys out here.
So here is why:
I have a dataset (data) which contains two variables: A (Numbers) and B (cell array).
Unfortunately I can't even reconstruct the problem nevertheless my imported table looks like this:
data=dataset;
data.A = [1;1;3;3;3];
data.B = ['A';'A';'BUU';'BUU';'A'];
where data.B is of the type 5x1 cell which I can't reconstruct
all I want now is the unique rows like
ans= [1 A;3 BUU;3 A]
the result should be in a dataset or just two vectors where the rows are equivalent.
but unique([dataA dataB],'rows') can't handle cell arrays and I can't find anywhere in the www how I simple convert the cell array B to a vector of strings (does it exist?).
cell2mat() didn't work for me, because of the different word length ('A' vs 'BUU').
Though, two things I would love to learn: Making an 5x1 cell to an string vector
and find unique rows out of numbers and strings (or cells).
Thank you very much!
Cheers Dominik
The problem is that the A and B fields are of a different type. Although they could be concatenated into a cell array, unique can't handle that. A general trick for cases like this is to "translate" elements of each field (column) to unique identifiers, i.e. numbers. This translation can be done applying unique to each field separately and getting its third output. The obtained identifiers can now be concatenated into a matrix, so that each row of this matrix is a "composite identifier". Finally, unique with 'rows' option can be applied to this matrix.
So, in your case:
[~, ~, kA] = unique(data.A);
[~, ~, kB] = unique(data.B);
[~, jR] = unique([kA kB], 'rows');
Now build the result as (same format as data)
result.A = data.A(jR);
result.B = data.B(jR);
or as (2D cell array)
result = cat(2, mat2cell(data.A(jR), ones(1,numel(jR))), data.B(jR));
Here is my clumpsy solution
tt.A = [1;1;3;3;3];
tt.B = {'A';'A';'BUU';'BUU';'A'};
Convert integers to characters, then merge and find unique strings
tt.C = cellstr(num2str(tt.A));
tt.D = cellfun(#(x,y) [x y],tt.C,tt.B,'UniformOutput',0);
[tt.F,tt.E] = unique(tt.D);
Display results
tt.F
I have a 3 sets of CT data each in it's own 700x700x512 array and I want to merge them into just one single array.
I had a look at the cat() function but didn't really understand how you set the dim variable- i.e. say for two simple 3x3x3 arrays, A & B, can I use AB_merge = cat(dim, A, B);
Thanks for any help!
The dim variable sets along which dimension you want to concatenate the images.
So if you want them 'on top of each other' that is along the 3rd dimensions:
AB_merge=cat(3, A, B);
If it is side by side along the x-axis:
AB_merge=cat(1, A, B);
etc.
Let's say, I have an M x N matrix. Now, I want to insert a constant M x 1 column vector (say all 1's) in between each of the N columns. Therefore, my resulting matrix would be of dimension (M x (2*N-1)), with every other column being 1's.
Is there an easy way to do that?
Vertically concatenate a matrix of ones, reshape, and cut off the last column of ones. For a matrix A:
B = reshape([A; ones(size(A))],size(A,1),[]);
B(:,end)=[]
Here is another way to do it, using the possibility of out of bounds indexing in assignments:
M(:,1:2:end*2)=M;
M(:,2:2:end)=1
If you don't mind creating a temporary matrix, one way to do it would be to do the following:
old_matrix = rand(M,N); % Just for example
new_matrix = ones(M,2*N-1);
new_matrix(:,1:2:end) = old_matrix;
Note that for an arbitrary constant matrix, you could replace the second line with the following:
new_matrix = repmat(const_array,1,2*N-1);