My variables and their values, in the if condition statement
leftoverROI1s{1}= [11 15];
missinglabelsinimage{1} is an empty matrix.
I want to execute a for loop only if both my conditions in the if statement are true, i.e.:
if ~isempty(leftoverROI1s{1}) && ~isempty(missinglabelsinimage{1})
for % loop for each element in non-empty `missinglabelsinimage` structure array.
% Add a scalar to each element of non-empty `missinglabelsinimage` structure array
...
end % end for loop
end % end if
My program control is going into for loop (which I expect, it shouldn't if there is an empty missinglabelsinimage{1}) and the control is working on missinglabelsinimage{1} (empty matrix), which obviously gives me an error as I am trying to add a scalar to my 'non-empty' missinglabelsinimage{1}.
I am not able to understand the error in my if condition. Any help would be appreciated.
PS: I checked the above variables
~isempty(missinglabelsinimage{1})
ans =
0
~isempty(leftoverROI1s{1})
ans =
1
missinglabelsinimage{1}
ans =
Empty matrix: 1-by-0
I suspect there is a typo somewhere in code that you are not showing. Reducing your example to its most basic form (always a good idea to try to find a bug):
a = [];
b = [1 2 3];
display(~isempty(a))
display(~isempty(b))
if ~isempty(a) && ~isempty(b)
disp('we passed the if')
else
disp('we are in the else')
end
Results in the output
ans =
0
ans =
1
we are in the else
Exactly as you would expect. If you get something different, then the code you are using isn't the code you are showing... is there a similar (mistyped) variable somewhere? Try doing a clear all, then run a minimal example that reproduces your problem.
Related
This is a function that checks if the array that is inputted is a square matrix. The function is doing what I want, namely checking if the array is square, but it also outputs the logical array that I am using to check if the number of rows equals the number of columns.
function isSquare = checkSquare(x)
[rnum, cnum] = size(x);
isSquare = rnum == cnum;
if isSquare == 1
fprintf('True')
else
fprintf('False')
end
end
I think it's because you're running the function without putting a semicolon at the end.
>> checksquare(zeros(4,4))
True
ans =
logical
1
>>
Instead, try this.
>> checksquare(zeros(4,4));
True>>
It would be nicer for the formatting to print a newline character after True or False. Change fprintf('True') to fprintf('True\n') and fprintf('False') to fprintf('False\n') and you'll get the following result.
>> checksquare(zeros(4,4));
True
>>
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.
Is there something inbuilt in MATLAB which functions similar to the SQL COALESCE function. I want that function to return the first 'existing' value from all the arguments.
For example,
clear A B; C=10; COALESCE(A,B,C)
should return value of C (because A and B are unassigned/don't exist).
I know it would be very easy to code, and I am just being lazy here. But, I would be surprised if MATLAB doesn't have a similar function.
As far as I know there is no built-in function for that. But you can easily write your own.
Note that it is not possible in Matlab to pass a variable that has not been defined prior of using it. Therefore your proposed call clear A B; C=10; COALESCE(A,B,C) is invalid and will throw an error. Instead we can define an empty variable using var=[].
The following code creates two empty variables A, B and and assigns C=10. Inside the function coalesce we assume at the beginning that all variables are empty. In the for-loop we return the first non-empty variable. In the version without for-loop we get the index of the first non-zero element and then return the corresponding content of the cell if a non-zero element exists.
If you want the function to be accessible from everywhere within Matlab, see the documentation here.
function testcoalesce
A = [];
B = [];
C = 10;
COALESCE(A,B)
COALESCE(A,B,C)
end
% with for-loop (much faster)
function out = COALESCE(varargin)
out = [];
for i = 1:length(varargin)
if ~isempty(varargin{i})
out = varargin{i};
return;
end
end
end
% without for-loop (slower)
function out = COALESCE(varargin)
out = [];
ind = find(cellfun('isempty', varargin)==0, 1);
if ~isempty(ind);
out = varargin{ind};
end
end
The output is as expected:
ans =
[]
ans =
10
Timing the two functions showed, that the first solution using the for-loop is approximately 48% faster than the function without loop.
(10 samples, 1'000'000 iterations, 3 variables & 20 variables)
Consider the following MATLAB struct:
a(1).num=1; a(2).num=2; a(3).num=3;
The thing I want to do is to replace some of the elements of num with the old value minus a (scalar) number. For example, I would like to subtract 1 from a(2).num and a(3).num.
I already tried different ways:
a(2:3).num=a(2:3).num-1;
??? Error using ==> minus Too many input arguments.
Next try:
>>a(2:3).num=[a(2:3).num]-1;
??? Insufficient outputs from right hand side to satisfy comma separated list
expansion on left hand side. Missing [] are the most likely cause.
And last:
>> [a(2:3).num]=[a(2:3).num]-1;
??? Error using ==> minus
Too many output arguments.
arrayfun couldn´t help either.
Probably there is a quite easy answer to this question, but I couldn´t find any.
Easiest is a two-line solution:
C = num2cell([a(2:3).num]-1);
[a(2:3).num] = C{:}
Nicest is to have a function like deal, but with a function applied to each argument:
function varargout = fcnDeal(varargin)
%// (Copied from MATLAB's deal()
if nargin==1,
varargout = varargin(ones(1,nargout));
else
if nargout ~= nargin-1
error('fcnDeal:narginNargoutMismatch',...
'The number of outputs should match the number of inputs.')
end
%//...Except this part
varargout = cellfun(varargin{1}, varargin(2:end), 'UniformOutput', false);
end
end
Then what you want to do is just a matter of
[a(2:3).num] = fcnDeal(#(x)x-1, a(2:3).num)
You can manipulate them in the loop
index = [1,2]
for i = index
a(i).num = a(i).num - 1;
end
I'm trying to write some code to calculate a cumulative distribution function in matlab. When I try to actually put my results into an array it yells at me.
tempnum = ordered1(1);
k=2;
while(k<538)
count = 1;
while(ordered1(k)==tempnum)
count = count + 1;
k = k + 1;
end
if(ordered1(k)~=tempnum)
output = [output;[(count/537),tempnum]];
k = k + 1;
tempnum = ordered1(k);
end
end
The errors I'm getting look like this
??? Error using ==> vertcat
CAT arguments dimensions are not consistent.
Error in ==> lab8 at 1164
output = [output;[(count/537),tempnum]];
The line to add to the output matrice was given to me by my TA. He didn't teach us much syntax throughout the year so I'm not really sure what I'm doing wrong. Any help is greatly appreciated.
If you're building the matrix output from scratch, you should make sure it hasn't already been initialized to anything. To do this, you can set it to the empty matrix at the beginning of your code:
output = [];
Also, if you know how large output is going to be, your code will run more efficiently if you preallocate the array output and index into the array to assign values instead of appending values to it. In your case, output should have the same number of rows as there are unique values in the array ordered1, so you could use the function UNIQUE to preallocate output:
nRows = numel(unique(ordered1)); %# Get the number of unique values
output = zeros(nRows,2); %# Initialize output
You would then have to keep a separate counter (say r) to track which index into output you will be adding to next:
...
output(r,:) = [count/537 tempnum]; %# Overwrite a row in output
r = r+1; %# Increment the row index
...
Some additional advice...
Even if you solve the error you are getting, you're going to run into more with the code you have above:
I believe you are actually computing a probability density function (or PDF) with your code. In order to get the cumulative distribution function (or CDF), you have to perform a cumulative sum over the final values in the first column of output. You can do this with the function CUMSUM:
output(:,1) = cumsum(output(:,1));
Your loop will throw an error when it reaches the last element of ordered1. The value of k can become 538 in your inner while loop, which will then cause an error to be thrown when you try to access ordered1(k) anywhere. To get around this, you will have to add checks to the value of k at a number of points in your code. One such point is your inner while loop, which can be rewritten as:
while (k <= 537) && (ordered1(k) == tempnum)
count = count + 1;
k = k + 1;
end
This solution uses the short-circuit AND operator &&, which will first check if (k <= 537) is true or false. If it is false (i.e. k > 537), the second logical check is skipped since its result doesn't matter, and you avoid the error that would result from evaluating ordered1(k).
Bonus MATLAB coolness...
MATLAB has a lot of cool functions that can do a lot of the work for you. One such function is ACCUMARRAY. Your TA may want you to do things using loops like you have above, but you can actually reduce your whole code to just a few lines like so:
nValues = numel(ordered1); %# Get the number of values
p = accumarray(ordered1,ones(size(ordered1)))./nValues; %# Create a PDF
output = [cumsum(p) unique(ordered1)]; %# Create the CDF output