I have a cell array and a vector, and I want to assign each coordinate of the vector to a different cell, in the same location.
For example, the j coordinate in a vector becomes the (k,l) coordinate in the (j,1) cell. In pseudo matlab it would look like this:
myCell{:,1}(k,l)=myVector;
Is there a good way to do that without just looping? (performance is an issue.)
a small example:
myCell=cell(2,4);
myV=[1;2];
%what I wish to change:
for j=1:size(myV,1)
myCell{j,1}(1,1)=myV(j)
end
Thanks in advance!
Depending on the data type in your myVector you'll end up using one of the two following commands.
mat2cell or num2cell
The help pages in Matlab give great detail on the different ways to call the functions, just in case you want to do some fancy grouping of the data and such.
mat2cell: http://www.mathworks.com/help/techdoc/ref/mat2cell.html
num2cell: http://www.mathworks.com/help/techdoc/ref/num2cell.html
Sample Code:
myCell=cell(2,4);
myV=[1;2];
% %what I wish to change:
% for j=1:size(myV,1)
% myCell{j,1}(1,1)=myV(j)
% end
myCell(:,1) = num2cell(myV);
Related
I have text files that contain two columns with numbers. Over a for loop, I store the first and second column as X(n) and Y(n) respectively (as floats), n being the iteration number.
Let's say that I don't know how many files I have and that the length/range of the data is variable.
Is there a way to create a sort of dynamic variable so I can use it as an input to graphically represent the data like
plot(dynamic_variable)
instead of writing per hand
plot(X1,Y1,X2,Y2,...,XN,YN)
I know there should be the possibility to interpolate the data (since the files haven't the same length/range) so it is possible to create two matrices, let say XM and YM, and finally write (XM,YM), where
XM = [X1_intrpl X2_intrpl ... XN_intrpl]
YM = [Y1_intrpl Y2_intrpl ... YN_intrpl].
Is there a more direct way to do it?
I am far from being an expert: so I would also appreciate any comment and/or criticism on my idea/approach.
The Matlab plot function does not seem to support what you are looking for. I guess you have already checked the documention on the plot command here:
https://de.mathworks.com/help/matlab/ref/plot.html?requestedDomain=www.mathworks.com
What you can do is write your own plot function that takes both matrices as parameters.
In the function you would loop over the pairs in the matrices plotting them using hold on to display all the data in one plot.
One option would be reading in each set of X(n) and Y(n) into a cell array such that,
X{1} = X1
Y{1} = Y1
...
X{N} = XN
Y{N} = YN
Then to plot, rather than trying to merge everything into a single array, you can simply plot each set of X and Y one at a time onto the same figure.
%Instead of:
%plot(X1,Y1,X2,Y2,...,XN,YN)
%Use:
figure()
hold on
for i=1:N
plot(X{i},Y{i})
end
I'm having a bit of trouble trying to make a 2D plot of a function depending on only one variable. Cutting a long story short, the function can only accept scalar values; it will not accept vectors. Hence it is not possible to use, for example, plot(vector, function(vector)), for a range of independent values vector. I've tried to use loop also, but my knowledge is limited, and it hasn't worked in any case.
To summarise: I want to plot function(x) vs x, however function may only have a scalar input, so taking x=-10:1:10 and then plotting it against function wouldn't work.
Can anybody point me in the right direction?
vector = -10:10 % set up your vector
output = zeros(size(vector); % initialise the output
for ii = 1:numel(vector)% loop over all elements of your vector
output(ii) = function(vector(ii)); % feed the function a single element at a time
end
plot(vector,output) % Now you can plot the two vectors
I want to make a plot that discontinues at one point using Matlab.
This is what the plot looks like using scatter:
However, I would like to the plot to be a smooth curve but not scattered dots. If I use plot, it would give me:
I don't want the vertical line.
I think I can break the function manually into two pieces, and draw them separately on one figure, but the problem is that I don't know where the breaking point is before hand.
Is there a good solution to this? Thanks.
To find the jump in the data, you can search for the place where the derivative of the function is the largest:
[~,ind] = max(diff(y));
One way to plot the function would be to set that point to NaN and plotting the function as usual:
y(ind) = NaN;
plot(x,y);
This comes with the disadvantage of losing a data point. To avoid this, you could add a data point with value NaN in the middle:
xn = [x(1:ind), mean([x(ind),x(ind+1)]), x(ind+1:end)];
yn = [y(1:ind), NaN, y(ind+1:end)];
plot(xn,yn);
Another solution would be to split the vectors for the plot:
plot(x(1:ind),y(1:ind),'-b', x(ind+1:end),y(ind+1:end),'-b')
All ways so far just handle one jump. To handle an arbitrary number of jumps in the function, one would need some knowledge how large those jumps will be or how many jumps there are. The solution would be similar though.
you should iterate through your data and find the index where there is largest distance between two consecutive points. Break your array from that index in two separate arrays and plot them separately.
I have a matrix which is 1*1*10000, the slightly odd dimensions are the result of the matrix algebra used to calculate it.
I simply want to be able to plot the 10000 data points contained in it, but matlab seems unable to do it?
Can someone please tell me how I can plot the data?
Seems simple but I really can't figure out how to do it!
Baz
yes you need to reduce the dimensions to a vector:
A = zeros(1,1,100)
vector = squeeze(A(1,1,:))
as when you'd access the third dimension this would only return a 3D-Matrix again:
z = A(1,1,:)
would NOT work. So use squeeze() ;-) Then plot as usual.
Doc-Link: http://www.mathworks.de/de/help/matlab/ref/squeeze.html
And as Ander pointed out in comments, no need to give any dimensions, as it removes singleton-dimensions by itself. So just use vector = squeeze(A). MATLAB recognizes the way to go itself.
A question about matlab and randomisation of a 3d matrix respecting the rows and columns.
I have a n x n x s matrix M and I want to mess it up a bit, but with some control.
I can achieve my wish with a for loop
for j=1:size(M,3)
r=randperm(size(M,1));
random_M(:,:,j)=M(r,r,j);
end
Is there a way to perform this without having to loop over j? I need many randomisation iterations and could afford the benefits of indexing.
Cheers!
edit: Some more thoughts following Alexandrew's comments
I have created a function that randomises a squeezed version of M:
function randomMat=randomiseMat(Mat)
[rows,cols]=size(Mat);
r=randperm(rows);
randomMat=Mat(r,r);
then, using arrayfun I seem to get what I want:
randomM=arrayfun(#(x) randomiseMat(M(:,:,x)),1:size(M,3),'UniformOutput', false)
however, randomM is now a cell array of size (1,size(M,3)) with each cell containing randomised array.
Is there a way to make it in a 3d matrix just like the input M?
You can calculate all the values for r in one go, and then use arrayfun:
[nRows,nCols,nPages] = size(M);
[~,r]=sort(rand(nRows,nPages));
%# you should test on a realistic example whether a for-loop
%# isn't faster here
outCell = arrayfun(#(x) M(r(:,x),r(:,x),x), 1:nPages,'UniformOutput',false);
randomM = cat(3,outCell{:});