I have a variable classi which is composed out of cells (269x500), it can be found here http://ojtwist.be/data.mat . I'm trying to sum the rows of this matrix so that i get a vector of 269x1. I tried converting the variable to a matrix with cell2mat but this doesn't work. Or matlab sees the sign (-) as a seperate cell. Therefore i can't use sum(classi(:),2). My question is now, how can I do this efficiently ?
Thx
Here's how you could do it:
load data.mat
a = sum( cellfun(#str2double, classi), 2);
Related
I have a row cell vector M, containing matrices in each cell. Every matrix m (matrix inside the big matrix M) is made of 2 channels (columns), of which I only want to use the first.
The approach I thought about was going through each m, check if it has 2 channels, and if that is the case delete the second channel.
Is there a way to just slice it in matlab? or loop it and obtain the matrix M as the matrix m would disappear.
First code is:
load('ECGdata.mat')
I have the below.
when I double-click in one of the variable , here is what I can see:
As you can see the length of each matrix in each cell is different. Now let's see one cell:
The loop I'm trying to get must check the shape of the matrix (I'm talking python here/ I mean if the matrix has 2 columns then delete the second) because some of the variables of the dataframe have matrix containing one column (or just a normal column).
In here I'm only showing the SR variable that has 2 columns for each matrix. Its not the case for the rest of the variables
You do not need to delete the extra "channel", what you can do is quite simple:
newVar = cellfun(#(x)x(:,1), varName, 'UniformOutput', false);
where varName is SR, VF etc. (just run this command once for each of the variables you load).
What the code above does is go over each element of the input cell (an Nx2 matrix in your example), and select the first column only. Then it stores all outputs in a new cell array. In case of matrices with a single column, there is no effect - we just get the input back.
(I apologize in advance if there is some typo / error in the code, as I am writing this answer from my phone and cannot test it. Please leave a comment if something is wrong, and I'll do my best to fix it tomorrow.)
I have a matrix with a large number of rows. I have another matrix that I will loop through one row at a time. For each row in the second matrix, I need to look for similar rows in the first matrix. Once all the similar rows are found, I need to know the row numbers of the similar rows. These rows will almost never be exact, so ismember does not work.
Also, the solution would preferably (not necessarily, however) give some way to set a level of similarity that would trigger the code to say it is similar and give me the row number.
Is there any way to do this? I've looked around, and I can't find anything.
You could use cosine distance, which finds the angle between two vectors. Similar vectors (in your case, a row and your comparison vector) have a value close to 1 and dissimilar vectors have a value close to 0.
function d = cosSimilarity(u, v)
d = dot(u,v)/(norm(u)*norm(v));
end
To apply this function to each to all pairs of rows in the matrices M and V you could use nested for loops. Hardly the most elegant, but it will work:
numRowsM = size(M, 1)
numRowsV = size(V, 1)
similarThresh = .9
for m = 1:numRowsM
for v = 1:numRowsV
similarity = cosSimilarity(V(v,:), M(m, :))
% Notify about similar rows
if similarity > similarThresh
disp([num2str(m) ' is similar to a row in V'])
end
end
end
Instead of nested for loops, there are definitely other ways. You could start by looking at the solution from this question, which will help you avoid the loop by converting the rows of the matrix into cells of a cell array and then applying the function with cellfun.
i have two matrices
r=10,000x2
q=10,000x2
i have to find out those rows of q which are one value or both values(as it is a two column matrix) different then r and allocate them in another matrix, right now i am trying this.i cannot use isequal because i want to know those rows
which are not equal this code gives me the individual elements not the complete rows different
can anyone help please
if r(:,:)~=q(:,:)
IN= find(registeredPts(:,:)~=q(:,:))
end
You can probably do this using ismember. Is this what you want? Here you get the values from q in rows that are different from r.
q=[1,2;3,4;5,6]
r=[1,2;3,5;5,6]
x = q(sum(ismember(q,r),2) < 2,:)
x =
3 4
What this do:
ismember creates an array with 1's in the positions where q == r, and 0 in the remaining positions. sum(.., 2) takes the column sum of each of these rows. If the sum is less than 2, that row is included in the new array.
Update
If the values might differ some due to floating point arithmetic, check out ismemberf from the file exchange. I haven't tested it myself, but it looks good.
I am using a cell array to contain 1x2 vectors of grid locations in the form [row, col].
I would like to check if another grid location is included in this cell array.
Unfortunately, my current code results in an error, and I cannot quite understand why:
in_range = ismember( 1, ismember({[player.row, player.col]}, proximity(:,1)) );
where player.row and player.col are integers, and proximity's first column is the aforementioned cell array of grid locations
the error I am receiving is:
??? Error using ==> cell.ismember at 28
Input must be cell arrays of strings.
Unfortunately, I have not been able to find any information regarding using ismember() in this fashion, only with cell arrays as strings or with single integers in each cell rather than vectors.
I have considered converting using num2str() and str2num(), but since I must perform calculations between the conversions, and due to the number of iterations the code will be looped for (10,000 loops, 4 conversions per loop), this method seems prohibitive.
Any help here would be greatly appreciated, thank you
EDIT: Why does ismember() return this error? Does it treat all vectors in a cell array as string arrays?
EDIT: Would there be a better / more efficient method of determining if a 1 is in the returned vector than
ismember( 1, ismember(...))?
I'm short of time at the moment (being Chrissy eve and all), so this is going to have to be a very quick answer.
As I understand it, the problem is to find if an x y coordinate lies in a sequence of many x y coordinates, and if so, the index of where it lies. If this is the case, and if you're interested in efficiency, then it is wasteful to mess around with strings or cell arrays. You should be using numeric matrices/vectors for this.
So, my suggestion: Convert the first row of your cell array to a numeric matrix. Then, compare your x y coordinates to the rows of this numerical matrix. Because you only want to know when both coordinates match a row of the numerical matrix, use the 'rows' option of ismember - it will return a true only on matching an entire row rather than matching a single element.
Some example code that will hopefully help follows:
%# Build an example cell array with coordinates in the first column, and random strings in the second column
CellOfLoc = {[1 2], 'hello'; [3 4], 'world'; [5 6], '!'};
%# Convert the first column of the cell array to a numerical matrix
MatOfLoc = cell2mat(CellOfLoc(:, 1));
%# Build an example x y coordinate location to test
LocToTest = [5 6];
%# Call ismember, being sure to use the rows option
Index = ismember(MatOfLoc, LocToTest, 'rows');
Note, if the indices in your cell array are in string form, then obviously you'll also need a call to str2num in there somewhere before you call ismember.
One other thing, I notice you're a new member, so welcome to the site. If you think this response satisfactorily answered your question, then please mark the question answered by clicking the tick mark next to this response.
I would like to generate all possible combinations for selecting rows in batches of lets say 'k' size. For example, matrix A has 3 rows and I want all combinations for batch size 2, i.e. rows (1,2)(1,3)(2,3). What would be the simplest way to do it? Then I would like use them for some operation like myfunction();
I think nchoosek function does the trick of selecting the combination but then how can I use each row of the output from nchoosek as index for my matrix?
If you want to use each combination one by one you can do something like this:
A = rand(3);
comb = nchoosek(length(A), 2);
for i = 1:size(comb, 1)
myfunction(A(comb(i, :), :));
end
A(comb(i, :)) is a k x n matrix (here 3 x 2) corresponding to the i-th combination of rows.