I would like to plot connected points in MATLAB.
My connected points come from connecting objects of "stats", where each "stat" comes from a BW regionprops struct.
The code I have written works, but it suffers from a lot of "ugliness", which I couldnt fix even after trying various ways.
function plot_line( line )
a = cell2mat(line);
b = {a.Centroid};
matx = {};
maty = {};
for i = 1:size(b,2)
matx{end+1} = b{i}(1);
maty{end+1} = b{i}(2);
end
plot ( cell2mat(matx), cell2mat(maty) );
end
Can you help me make this code nicer? It's not critical, as my code works fine and as the lines are short (<100 points) the performance is not an issue.
It is just that it would be really nice to know how this tiny function should be written in the proper way, without for loops and 3 calls of cell2mat.
In my example:
line is a <1xn cell>,
line{1} has a property 'Centroid' and
line{i}.Centroid(1) are the x coordinates and
line{i}.Centroid(2) are the y coordinates.
Actually, all I need is plotting line{i}.Centroid(1), line{i}.Centroid(2) for i = 1:size(line,2), but I don't know how.
Instead of creating a cell array b, you can create a numerical array directly, by catenating using CAT:
tmp = cat(1,line{:});
coordinates = cat(1,tmp.Centroid);
plot(coordinates(:,1),coordinates(:,2))
EDIT
If you want to keep it really short (i.e. even shorter than #Amro's solution you can use CELLFUN like this in order get a one-liner:
plot(cellfun(#(x)x.Centroid(1),line),cellfun(#(x)x.Centroid(2),line))
Example:
line = repmat({struct('Centroid',[1 2])},1,5); %# similar to the data you have
%# extract x/y coordinates
x = cellfun(#(s)s.Centroid(1),line)
y = cellfun(#(s)s.Centroid(2),line)
%# plot
plot(x,y)
You could also do it as:
xy = cell2mat(cellfun(#(s)s.Centroid, line, 'UniformOutput',false)');
plot(xy(:,1),xy(:,2))
Related
First of all, I just want to say that I'm not that used to using matlab, but I need for an assignment, I'm supposed to create a "brownian movement". My code is currently looking like this:
clf
hold on
prompt = 'Ge ett input';
size = input(prompt) ;
numParticles = input('Ange antal partiklar');
axis([-size size -size size]);
Part = [];
color = 'brkgmyco';
for i = drange(1:numParticles)
Part = [Part [0;0]];
end
for i = drange(1:200)
dxdy = randn(2,numParticles);
k = Part
Part = Part + dxdy;
My concern is how to print, I would even want like a small delay on every print, so you really can see what's happening for the assignment, is this possible to achieve from the code I've written for now or should anything be changed? Thanks in advance!
Here are some basic problems with your code, regardless of what you are trying to do:
You use size as a variable name. Doing so overrides MATLAB's function size.
The function zeros creates an array initialized by zeros, no need for a loop for that.
Instead of calculating randn for 200 times in a loop, you can do it once, with dxdy = randn(2,numParticles,200) and then simply refer to dxdy(:,:,i) within the loop.
The same holds for summation. Instead of summing within a loop to get the cumulative sum, use cumsum like Part = cumsum(randn(2,numParticles,200),3); and then refer to Part(:,:,i), within the loop.
Now to your task. You said you want to know how to print, but I believe you want to plot because you use some commands like axis, clf and hold, that refer to graphic objects. However, you never really do plot anything.
The basic and general function for plotting in 2D is plot, but there are many other more specific functions. One of them is scatter, and it has a sister function gscatter, that takes triples of x, y and groupand plot each (x(k),y(k)) colored by their group(k).
This code plots the particles on an axes, and animate their movement:
prompt = 'Ge ett input';
scope = input(prompt) ;
numParticles = input('Ange antal partiklar');
N = 500;
Part = cumsum(randn(2,numParticles,N)*scope/100,3);
h = gscatter(Part(1,:,1),Part(2,:,1),1:numParticles);
axis([-scope scope -scope scope]);
legend off
for k = 2:N
for p = 1:numParticles
h(p).XData = Part(1,p,k);
h(p).YData = Part(2,p,k);
end
drawnow
end
Is this what you look for?
I am working on a code to extract my AR(1)-GARCH(1) parameter, which I estimated using an AR(1)-GJR(1,1) model to individual matrices so that I can use them as variables in my calculations. As I have 16 time series variables, I combine the code with a loop in the following way:
for i=1:nIndices
AA_ARCH(:,i) = cell2mat(fit{i}.Variance.ARCH)';
end;
My problem is that for some variables is are no for AA_ARCH(:,i) the dimension is lower than nIndices. Naturally, when I try to export the estimates in the loop which specified the dimension of (:,i) and nIndices matlab reports a dimension mismatch. I would like to tell Matlab to replace the NaN with 0 instead of leaving the spot empty so that it is able to produce a (1,nIndices) matrix from AA_ARCH.
I thought of something like the this:
fit{i}.Variance.Leverage(isnan(fit{i}.Variance.Leverage))=0
but I wasn't able to combine this part with the previous code.
I would be very happy about any hints!
Best, Carolin
UPDATE:
Here is a fully a runnable version of my code which produces my problem. Notice that the code produces a dimension mismatch error because there is no ARCH and GARCH estimate in the fit.gjr(1,1) for time series 1. For these missing values I would like to have 0 as a placeholder in the extracted matrix.
returns = randn(2,750)';
T = size(returns,1);
nIndices = 2;
model = arima('AR', NaN, 'Variance', gjr(1,1));
residuals = NaN(T, nIndices);
variances = NaN(T, nIndices);
fit = cell(nIndices,1);
options = optimset('fmincon');
options = optimset(options, 'Display' , 'off', 'Diagnostics', 'off', ...
'Algorithm', 'sqp', 'TolCon' , 1e-7);
for i = 1:nIndices
fit{i} = estimate(model, returns(:,i), 'print', false, 'options', options);
[residuals(:,i), variances(:,i)] = infer(fit{i}, returns(:,i));
end
for i=1:nIndices
AA_beta(:,i) = cell2mat(fit{i}.AR)';
AA_GARCH(:,i) = cell2mat(fit{i}.Variance.GARCH)';
AA_ARCH(:,i) = cell2mat(fit{i}.Variance.ARCH)';
AA_Leverage(:,i) = cell2mat(fit{i}.Variance.Leverage)';
end;
I have some general things to say about the code, but first a solution to your problem:
You can put a simple if/else structure in your loop to handle the case of an empty array:
for ind1=1:nIndices
AA_beta(:,ind1) = cell2mat(fit{ind1}.AR)'; %//'
%// GARCH
if isempty(cell2mat(fit{ind1}.Variance.GARCH)') %//'
AA_GARCH(1,ind1) = 0;
else
AA_GARCH(:,ind1) = cell2mat(fit{ind1}.Variance.GARCH)'; %//'
end
%// ARCH (same exact code, should probably be exported to a function)
if isempty(cell2mat(fit{ind1}.Variance.ARCH)') %//'
AA_ARCH(1,ind1) = 0;
else
AA_ARCH(:,ind1) = cell2mat(fit{ind1}.Variance.ARCH)'; %//'
end
AA_Leverage(:,ind1) = cell2mat(fit{ind1}.Variance.Leverage)'; %//'
end;
Side note: I initially tried something like this: soz = #(A)isempty(A)*0+~isempty(A)*A; as an inline replacement for the if/else, but it turns out that MATLAB doesn't handle [] + 0 the way I wanted (it results in [] instead of 0; unlike other languages like JS).
As for the other things I have to say:
I am a firm supporter of the notion that one shouldn't use i,j as loop indices, as this may cause compatibility problems in some cases where complex numbers are involved (e.g. if you loop index is i then 1*i now refers to the loop index instead of to the square root of -1).
Part of your problem was that the arrays you were writing into weren't preallocated - which also means the correct datatype was unknown to MATLAB at the time of their creation. Besides the obvious performance hit this entails, it could also result in errors like the one you encountered here. If, for example, you used cells for AA_beta etc. then they could contain empty values, which you could later replace with whichever placeholder your heart desired using a combination of cellfun and isempty. Bottom line: lint (aka the colorful square on the top right of the editor window) is your friend - don't ignore it :)
I was trying to plot function return values, one based on another. My function definition is:
function [final_speed, voltage] = find_final_speed(simulink_output)
As you can see, it returns two variables. I need a matrix that looks like this:
final_speed_1 voltage_1
final_speed_2 voltage_1
final_speed_3 voltage_1
final_speed_4 voltage_1
final_speed_5 voltage_1
In the end, voltages should be plotted on X axis, speeds on Y axis.
I originally tried this:
speedpervoltage = [find_final_speed(DATA_1); find_final_speed(DATA_2); ... ];
But that would only result in this matrix, all voltage info gone:
final_speed_1
final_speed_2
...
After all google searches and attempts failed, I did this:
[s1 v1] = find_final_speed(DATA_1);
[s2 v2] = find_final_speed(DATA_2);
[s... v...] = find_final_speed(DATA_...);
speedpervoltage = [0 0;s1 v1;s2 v2;s... v....;];
% Just contains the figure call along with graph properties.
plot_speedpervoltage(speedpervoltage);
This is really not optimal or practical solution. How can I do this more dynamically? Ideally, I'd like to have function create_speedpervoltage which would take array of data matrixes as argument:
plot_speedpervoltage(create_speedpervoltage([DATA_1 DATA_2 ...]));
if you know how many datasets you have, you encapsulate everything in a for loop like this:
Data = [DATA_1, DATA_2,....DATA_N] ;
outMat = [] ;
for i = 1 : length (Data)
[s v] = find_final_speed(Data(i));
outMat = [outMat ; s,v]
end
There is an easy way of doing this in Matlab. This answer is different from User1551892's answer because it doesn't dynamically reallocate the variable thus resulting in faster performance. The code is as follows.
% Declare Return Vectors
final_speed = zeros(20,1);
voltage = zeros(20,1);
% Loop through each data point
for i = 1: length( data )
[final_speed(i,:),voltage(i,:)] = find_final_speed( data(i) );
end
Now this assumes that data is a vector with each element corresponding to final and voltage speeds.
EDIT:
Another method to improve the speed even more is using arrayfun. Assuming your data is 1D, by feeding in the function as a handle into arrayfun, you can replace the 3 line loop with this line and preallocation with this code, which should give you even better performance and less lines.
[final_speed,voltage] = arrayfun( #find_final_speed, data );
Here is a solution with cellfun.
[s, v] = cellfun(#find_final_speed, [{DATA_1}, {DATA_2},... {DATA_N}]);
speedpervoltage = [s(:) v(:)];
I feel dumb even having to ask this, it really should be dead simple, but being new to MatLab I'd like to know how a more experienced person would do it.
Simple problem; I need to find some regions in multiple images, correlate them by position, save those regions of interest, and use them later. One way to do that would be to store the regions in a vector.
%% pseudo code
regions = [];
for i = some_vector_of_images
% segment, get mask
% find regions
cc = bwconncomp(mask);
stats = regionprops(cc, 'all');
% correlate against known x/y
% save for later
regions[index++] = stats;
end
% use 'regions'
However, the array declaration is problematic. Its default type is double, so that won't work (can't assign a struct to an element). I've tried struct.empty, but the array is not resizable. I've tried a cell array, but I get a similar error (Conversion to cell from struct is not possible.)
Really, I just need a way to have some collection declared prior to the loop that will hold instances of these structures. Again, pretty noobish question and slightly embarrassed here... please take pity.
See if using struct2cell helps you with this. Give this pseudo-code a try -
regions = cell(num_of_images,1) %// This will be before the loop starts
...
regions[index++] = {struct2cell(stats)} %// Inside the loop
Please not that this a pseudo-code, so square brackets and ++ won't work.
Thus, the complete version of pseudo-code would be -
%%// --- pseudo code
%// Without this pre-allocation you would get the error -
%%// "Conversion to cell from struct is not possible"
regions = cell(numel(some_vector_of_images),1)
for i = some_vector_of_images
% segment, get mask
% find regions
cc = bwconncomp(mask);
stats = regionprops(cc, 'all');
% correlate against known x/y
% save for later
regions(i) = {struct2cell(stats)}
end
You can cast your empty array to a structure array by appending a structure. Replace regions[index++] = stats; with
regions = [regions, stats];
This line will continue to build the array within the loop. This idiom is generally frowned on in MATLAB because a new array needs to be created each loop.
Another method is to preallocate the array with a template structure, using repmat.
stats = some_operations_on(some_vector_of_images(1));
regions = repmat(stats, numel(some_vector_of_images), 1);
and within the loop, assign with
regions(i) = stats;
In this scenario, typically I just don't preallocate at all, or use a cell-cat pattern.
Not initializing
This one doesn't initialize the struct array, but works fine. Make sure i is an index of each element in this case.
for i = 1:numel(some_vector_of_images)
% mask = outcome of some_vector_of_images(i)
cc = bwconncomp(mask);
regions(i) = regionprops(cc, 'all');
end
cell-cat pattern
This one catches results in a cell array, and concatenates all elements at the end.
regions = cell(numel(some_vector_of_images), 1);
index = 1;
for i = some_vector_of_images
% mask = outcome of i
cc = bwconncomp(mask);
regions{index} = regionprops(cc, 'all');
index = index + 1;
end
regions = cat(1, regions{:});
I have the following piece of code:
for query = queryFiles
queryImage = imread(strcat('Queries/', query));
queryImage = im2single(rgb2gray(queryImage));
[qf,qd] = vl_covdet(queryImage, opts{:}) ;
for databaseEntry = databaseFiles
entryImage = imread(databaseEntry.name);
entryImage = im2single(rgb2gray(entryImage));
[df,dd] = vl_covdet(entryImage, opts{:}) ;
[matches, H] = matchFeatures(qf,qf,df,dd) ;
result = [result; query, databaseEntry, length(matches)];
end
end
It is my understanding that it should work as a Java/C++ for(query:queryFiles), however the query appears to be a copy of the queryFiles. How do I iterate through this vector normally?
I managed to sort the problem out. It was mainly to my MATLAB ignorance. I wasn't aware of cell arrays and that's the reason I had this problem. That and the required transposition.
From your code it appears that queryFiles is a numeric vector. Maybe it's a column vector? In that case you should convert it into a row:
for query = queryFiles.'
This is because the for loop in Matlab picks a column at each iteration. If your vector is a single column, it picks the whole vector in just one iteration.
In MATLAB, the for construct expects a row vector as input:
for ii = 1:5
will work (loops 5 times with ii = 1, 2, ...)
x = 1:5;
for ii = x
works the same way
However, when you have something other than a row vector, you would simply get a copy (or a column of data at a time).
To help you better, you need to tell us what the data type of queryFiles is. I am guessing it might be a cell array of strings since you are concatenating with a file path (look at fullfile function for the "right" way to do this). If so, then a "safe" approach is:
for ii = 1:numel(queryFiles)
query = queryFiles{ii}; % or queryFiles(ii)
It is often helpful to know what loop number you are in, and in this case ii provides that count for you. This approach is robust even when you don't know ahead of time what the shape of queryFiles is.
Here is how you can loop over all elements in queryFiles, this works for scalars, row vectors, column vectors and even high dimensional matrices:
for query = queryFiles(:)'
% Do stuff
end
Is queryFiles a cell array? The safest way to do this is to use an index:
for i = 1:numel(queryFiles)
query = queryFiles{i};
...
end