I created a matfile in which I store data that are constantly overwritten by user behavior. This occurs in a function "test()".
n=1
while n < 5
myVal = double(Test704(1, 780, -1)) %Returns the user's behavior
if myVal == 1
n = n + 1 %"n" is the overwritten variable in the matfile
end
save('testSave1.mat') %The matfile
m = matfile('testSave1.mat')
end
Then, I want to display these data in another function (it is essential to have two separated functions) called "storageTest()". More particularly, storageTest() is a GUI function where I developped an uitable "t". So, I first call the function "test()" and give its output values as data of "t". Here is the code of the interesting part of "storageTest":
m = test()
d = [m.n]
t = uitable('Data',d, ...
'ColumnWidth',{50}, ...
'Position',[100 100 461 146]);
t.Position(3) = t.Extent(3);
t.Position(4) = t.Extent(4);
drawnow
This code executes only when "m = test()" running is over and displays me a tab in which I can see the final value of "n". However, I want my table to be displayed before and to see my value incrementing according to user's behavior.
I have searched on the web to solve my issue, but I cannot find any answer, is it possible to do such a thing?
Assuming I'm interpreting the question correctly, it should be fairly trivial to accomplish this if you initialize your table prior to calling test and then pass the handle to your table for test to update in the while loop:
For example:
function testGUI
% Initialize table
t = uitable('ColumnWidth',{50}, 'Position',[100 100 461 146]);
test(t)
function test(t)
n = 1;
while n < 5
n = n + 1;
t.Data = n;
pause(0.25); % Since we're just incrementing a number, a slight so we can actually see the change
end
When you run the above, you'll notice the data in your table iterating as expected.
excaza was a little faster in writing basically the same answer like me. As it looks a slightly different, I'll post it anyway.
function storagetest()
close all
f = figure;
data = [1];
t = uitable(f,'Data',data,'ColumnWidth',{50});
test()
end
function test()
% handle uitable
t = evalin('caller','t')
n = 1;
while n < 5
newVal = input('Enter a number:');
data = get(t,'Data');
set(t,'Data', [data; newVal]);
n = n + 1;
end
end
The "user behaviour" I imitated with the input function. The basic idea is to update your table from within test(). evalin you can use, if you don't want to pass parameters to test(), though passing the handle of the uitable directly is certainly the better option.
If you are working on a serious GUI project I highly recommend you reading this answer.
Related
I want to assign one value to a list of objects in Matlab without using a for-loop (In order to increase efficiency)
Basically this works:
for i=1:Nr_of_Objects
Objectlist(i,1).weight=0.2
end
But I would like something like this:
Objectlist(:,1).weight=0.2
Which is not working. I get this error:
Expected one output from a curly brace or dot indexing expression, but there were 5 results.
Writing an array to the right hand side is also not working.
I`m not very familiar with object oriented programming in Matlab, so I would be happy if someone could help me.
Your looking for the deal function:
S(1,1).a = 1
S(2,1).a = 2
S(1,2).a = 3
[S(:,1).a] = deal(4)
Now S(1,1).a and S(2,1).a equal to 4.
In matlab you can concatenate several output in one array using []. And deal(X) copies the single input to all the requested outputs.
So in your case:
[Objectlist(:,1).weight] = deal(0.2)
Should work.
Noticed that I'm not sure that it will be faster than the for loop since I don't know how the deal function is implemented.
EDIT: Benchmark
n = 1000000;
[S(1:n,1).a] = deal(1);
tic
for ii=1:n
S(ii,1).a = 2;
end
toc
% Elapsed time is 3.481088 seconds
tic
[S(1:n,1).a] = deal(2);
toc
% Elapsed time is 0.472028 seconds
Or with timeit
n = 1000000;
[S(1:n,1).a] = deal(1);
g = #() func1(S,n);
h = #() func2(S,n);
timeit(g)
% ans = 3.67
timeit(h)
% ans = 0.41
function func1(S,n)
for ii=1:n
S(ii,1).a = 2;
end
end
function func2(S,n)
[S(1:n,1).a] = deal(2);
end
So it seems that using the deal function reduce the computational time.
total newbie here. I'm having problems looping a function that I've created. I'm having some problems copying the code over but I'll give a general idea of it:
function[X]=Test(A,B,C,D)
other parts of the code
.
.
.
X = linsolve(K,L)
end
where K,L are other matrices I derived from the 4 variables A,B,C,D
The problem is whenever I execute the function Test(1,2,3,4), I can only get one answer out. I'm trying to loop this process for one variable, keep the other 3 variables constant.
For example, I want to get answers for A = 1:10, while B = 2, C = 3, D = 4
I've tried the following method and they did not work:
Function[X] = Test(A,B,C,D)
for A = 1:10
other parts of the code...
X=linsolve(K,L)
end
Whenever I keyed in the command Test(1,2,3,4), it only gave me the output of Test(10,2,3,4)
Then I read somewhere that you have to call the function from somewhere else, so I edited the Test function to be Function[X] = Test(B,C,D) and left A out where it can be assigned in another script eg:
global A
for A = 1:10
Test(A,2,3,4)
end
But this gives an error as well, as Test function requires A to be defined. As such I'm a little lost and can't seem to find any information on how can this be done. Would appreciate all the help I can get.
Cheers guys
I think this is what you're looking for:
A=1:10; B=2; C=3; D=4;
%Do pre-allocation for X according to the dimensions of your output
for iter = 1:length(A)
X(:,:,iter)= Test(A(iter),B,C,D);
end
X
where
function [X]=Test(A,B,C,D)
%other parts of the code
X = linsolve(K,L)
end
Try this:
function X = Test(A,B,C,D)
% allocate output (it is faster than changing the size in every loop)
X = {};
% loop for each position in A
for i = 1:numel(A);
%in the other parts you have to use A(i) instead of just A
... other parts of code
%overwrite the value in X at position i
X{i} = linsolve(K,L);
end
end
and run it with Test(1:10,2,3,4)
To answer what went wrong before:
When you loop with 'for A=1:10' you overwrite the A that was passed to the function (so the function will ignore the A that you passed it) and in each loop you overwrite the X calculated in the previous loop (that is why you can only see the answer for A=10).
The second try should work if you have created a file named Test.m with the function X = (A,B,C,D) as the first code in the file. Although the global assignment is unnecessary. In fact I would strongly recommend you not to use global variables as it gets very messy very fast.
In my code, I have lots of places where I invoke functions of the form
X = f(X)
and X can be a rather large matrix. In my special case, I have mostly calls like
X = feval(somefunc, X)
or
X = obj.myfunc(X)
It would be bad if, every time the function is called, there is new space allocated for X. Is MATLAB smart enough to deal with such function calls? Is there a way to tell?
The answer to this question helps would help very much with a design descision. I like to program in object oriented style and if MATLAB is not smart enough for this, it might pay off for me to add another member for X in the class, although I would rather not do this otherwise.
Whether a copy is made of the input arguments or not when calling a function in MATLAB depends upon what happens inside of the function.
MATLAB uses a system referred to as copy-on-write. This means that if you pass a large variable to a function as an input, as long as you do not modify the variable within that function, the variable will not be copied into the workspace of the function and the function will instead read the data from it's current location in memory.
function Y = func(X)
Y = X + 1;
end
If you are modifying the variable within the function, then a copy of the input variable is made and placed into the local workspace of the function.
function X = func(X)
X = X + 1;
end
There is more information on Loren's Mathworks blog.
An easy way to determine if a copy of the data is made or not is to use the undocumented format debug mode which will show you where the data for a given variable is stored in memory.
format debug
%// Create a variable a and show where debug info
a = [1,2]
%// Structure address = 141f567f0
%// m = 1
%// n = 2
%// pr = 7f9540b85e20
%// pi = 0
%// 1 2
%// Assign b = a but don't modify
b = a
%// Structure address = 141f567f0
%// m = 1
%// n = 2
%// pr = 7f9540b85e20 <= POINTER TO DATA REMAINED UNCHANGED
%// pi = 0
%// 1 2
%// Modify (Will create a new copy)
b = b + 1
%// Structure address = 141f55b40
%// m = 1
%// n = 2
%// pr = 7f953bcf1a20 <= POINTER TO DATA CHANGED (COPY)
%// pi = 0
%// 2 3
If you prefer you can use this little anonymous function I've created to inspect the memory location of any particular variable.
memoryLocation = #(x)regexp(evalc('disp(x)'), '(?<=pr\s*=\s*)[a-z0-9]*', 'match')
a = [1,2];
memoryLocation(a)
%// 7f9540b85e20
b = a;
memoryLocation(b)
%// 7f9540b85e20
b = b + 1;
memoryLocation(b)
%// 7f953bcf1a20
As a bit of a side-note, I would recommend against using feval throughout your code and instead just use the function names directly.
I am trying to concatenate several structs. What I take from each struct depends on a function that requires a for loop. Here is my simplified array:
t = 1;
for t = 1:5 %this isn't the for loop I am asking about
a(t).data = t^2; %it just creates a simple struct with 5 data entries
end
Here I am doing concatenation manually:
A = [a(1:2).data a(1:3).data a(1:4).data a(1:5).data] %concatenation function
As you can see, the range (1:2), (1:3), (1:4), and (1:5) can be looped, which I attempt to do like this:
t = 2;
A = [for t = 2:5
a(1:t).data
end]
This results in an error "Illegal use of reserved keyword "for"."
How can I do a for loop within the concatenate function? Can I do loops within other functions in Matlab? Is there another way to do it, other than copy/pasting the line and changing 1 number manually?
You were close to getting it right! This will do what you want.
A = []; %% note: no need to initialize t, the for-loop takes care of that
for t = 2:5
A = [A a(1:t).data]
end
This seems strange though...you are concatenating the same elements over and over...in this example, you get the result:
A =
1 4 1 4 9 1 4 9 16 1 4 9 16 25
If what you really need is just the .data elements concatenated into a single array, then that is very simple:
A = [a.data]
A couple of notes about this: why are the brackets necessary? Because the expressions
a.data, a(1:t).data
don't return all the numbers in a single array, like many functions do. They return a separate answer for each element of the structure array. You can test this like so:
>> [b,c,d,e,f] = a.data
b =
1
c =
4
d =
9
e =
16
f =
25
Five different answers there. But MATLAB gives you a cheat -- the square brackets! Put an expression like a.data inside square brackets, and all of a sudden those separate answers are compressed into a single array. It's magic!
Another note: for very large arrays, the for-loop version here will be very slow. It would be better to allocate the memory for A ahead of time. In the for-loop here, MATLAB is dynamically resizing the array each time through, and that can be very slow if your for-loop has 1 million iterations. If it's less than 1000 or so, you won't notice it at all.
Finally, the reason that HBHB could not run your struct creating code at the top is that it doesn't work unless a is already defined in your workspace. If you initialize a like this:
%% t = 1; %% by the way, you don't need this, the t value is overwritten by the loop below
a = []; %% always initialize!
for t = 1:5 %this isn't the for loop I am asking about
a(t).data = t^2; %it just creates a simple struct with 5 data entries
end
then it runs for anyone the first time.
As an appendix to gariepy's answer:
The matrix concatenation
A = [A k];
as a way of appending to it is actually pretty slow. You end up reassigning N elements every time you concatenate to an N size vector. If all you're doing is adding elements to the end of it, it is better to use the following syntax
A(end+1) = k;
In MATLAB this is optimized such that on average you only need to reassign about 80% of the elements in a matrix. This might not seam much, but for 10k elements this adds up to ~ an order of magnitude of difference in time (at least for me).
Bare in mind that this works only in MATLAB 2012b and higher as described in this thead: Octave/Matlab: Adding new elements to a vector
This is the code I used. tic/toc syntax is not the most accurate method for profiling in MATLAB, but it illustrates the point.
close all; clear all; clc;
t_cnc = []; t_app = [];
N = 1000;
for n = 1:N;
% Concatenate
tic;
A = [];
for k = 1:n;
A = [A k];
end
t_cnc(end+1) = toc;
% Append
tic;
A = [];
for k = 1:n;
A(end+1) = k;
end
t_app(end+1) = toc;
end
t_cnc = t_cnc*1000; t_app = t_app*1000; % Convert to ms
% Fit a straight line on a log scale
P1 = polyfit(log(1:N),log(t_cnc),1); P_cnc = #(x) exp(P1(2)).*x.^P1(1);
P2 = polyfit(log(1:N),log(t_app),1); P_app = #(x) exp(P2(2)).*x.^P2(1);
% Plot and save
loglog(1:N,t_cnc,'.',1:N,P_cnc(1:N),'k--',...
1:N,t_app,'.',1:N,P_app(1:N),'k--');
grid on;
xlabel('log(N)');
ylabel('log(Elapsed time / ms)');
title('Concatenate vs. Append in MATLAB 2014b');
legend('A = [A k]',['O(N^{',num2str(P1(1)),'})'],...
'A(end+1) = k',['O(N^{',num2str(P2(1)),'})'],...
'Location','northwest');
saveas(gcf,'Cnc_vs_App_test.png');
I'm trying to create a function that reads in a field of a structure to create a vector of fields. I have a structure of the form:
subject(i).stride(j).strideLength
and there are 10 subjects, about 10 strides per subject. I can create a long vector of the strideLength of all subjects, all strides with code like this:
k = 1;
for i=1:10
for j=1:size(subject(i).stride, 2)
varVector(k) = subject(i).stride(j).strideLength;
k = k + 1;
end
end
however, there are a lot of different fields I want to do this with, and I'd like to do it with a function that I can call like this:
x(1) = groupData(strideLength);
but I can't figure out the syntax to append strideLength to subject(i).stride(j). within the above loop in a function. This is what I hoped would work and didn't:
function [varVector] = groupData(var)
%groupData returns a concatenated vector of a given variable (speed, etc.)
k = 1;
for i=1:10
for j=1:size(subject(i).stride, 2)
varVector(k) = subject(i).stride(j).var;
k = k + 1;
end
end
end
Any thoughts on how to do this right? Thanks in advance!
In your groupData function, pass in the field/variable name as a string
x(1) = groupData('strideLength');
Then in the body of the code, access this field as follows
varVector(k) = subject(i).stride(j).(var);
Try the above and see what happens!