I want to change a variable name before I export it to the global enviroment, the data is very large, meaning I can not copy it to another variable and delete the first one.
the data is loaded to certain variables and that I cannot change as well, it is used multiple times in differnet background jobs, so what I want to do is rename it and send it renamed so the jobs won't mix and after for the next job load and rename again etc.
basically is to do in the command window what I can do with the mouse in the workspace....
does anyone knows how to do it?
When assigning variable names, matlab uses a "lazy copy", so there is no reason why:
new_name = old_name;
clear old_name;
shouldn't work.
The only way that I can think of to do this without a memory copy would be to wrap the original data in an object that is a subclass of the handle class.
http://www.mathworks.co.uk/help/techdoc/matlab_oop/brfylzt-1.html
You can then 'copy' the handle class using normal syntax
classB=classA
..but you are only making an alias for the same data (changes to classB are reflected in classA). This is the closest thing in matlab to pointer-like semantics.
For example, create a file called myHandle and paste the following text to define the class . .
classdef myHandle < handle
properties
data
moreData
end
methods
end
end
You can then use this just like a regular structure. From the command line do ..
>> x = myHandle
x =
myHandle handle
Properties:
data: []
moreData: []
Methods, Events, Superclasses
... we can then populate the data . . .
>> x.data = [1 2 3 4];
>> x.moreData = 'efg';
... once the original object has been populated with data, an alias of the original data can be made by typing . .
>> y = x
The interesting thing happens to x when y is modified, i.e.
>> y.data = [33 44 55 66];
>> disp(x)
x =
myHandle handle
Properties:
data: [33 44 55 66]
moreData: 'f'
Methods, Events, Superclasses
You can even clear one of the alias names . .
clear x
..and the data will still be available in the other handle for the data, y. The memory is only freed when there are no more handles referring to it (when the reference count has reached zero).
Related
I would like to add the sums of 5 one-column arrays in Matlab. The catch is that depending on previous inputs, any of these arrays may or may not exist, thus throwing an error when I try to add the sums of these arrays for post-processing.
After doing some digging I found the following function which I can use to return a logical statement if a certain variable exists in the workspace:
exist('my_variable','var') == 1
I'm not sure this helps me in this case though - Currently the line in which I add the sums of the various arrays looks as follows:
tot_deviation = sum(var1) + sum(var2) + sum(var3) + sum(var4) + sum(var4);
Is there a short way to add only the sums of the existing arrays without excessive loops?
Any help would be appreciated!
You can use if statements:
if ~exist('var1','var'), var1 = 0;end
if ~exist('var2','var'), var2 = 0;end
if ~exist('var3','var'), var3 = 0;end
if ~exist('var4','var'), var4 = 0;end
tot_deviation = sum(var1) + sum(var2) + sum(var3) + sum(var4) + sum(var4);
To my knowledge there is no quick way to do this in matlab. It seems to me that, depending on the structure of your code, you have the following alternatives:
1- Initialize all your variables to column arrays of zeros with something like
var = zeros(nbLines, 1);
2- Put all your columns vectors side to side in a single array and the use tot_deviation = sum(sum(MyArray)); which will work no matter how many columns and lines there is in the array.
3- If you pass your variables to a function you can check the number of inputs arguments inside the function using 'nargin' and then only proceed to sum the right number of variables.
I would recommend using the second method for it seem to me that it is the one that allows you to take the most advantage of matlab's array system which good.
The most robust solution is to initialise all of your variables to 0 at the top of the function. Then there is no chance they don't exist, and they influence the summation correctly.
Alternatively...
You could (read: shouldn't) use a really nasty eval trick here for flexibility...
vars = {'var1','var2','var3','var4'};
tot = 0;
for ii = 1:numel(vars)
if exist(vars{ii}, 'var')
tot = tot + eval(var);
end
end
I say it's "nasty" because eval should be avoided (read the linked blog). The check on the variable name existence mitigates some of the strife, but it's still not ideal.
As suggested in the MathWorks blog on evading eval, a better option would be a struct with dynamic field names. You could use almost the same syntax as above, but replace the if statement with
if isfield( myStruct, vars{ii} )
tot = tot + myStruct.(vars{ii});
end
This will avoid dynamically named variables and keep your workspace clean!
I need to create structures inside the base workspace from inside one of my functions and populate them with values, the problem is I don't explicitly know the names of the structures. Why? My model uses from workspace blocks, 2D arrays need structure form, as per Mathworks documentation. See below.
%some function
function [SimulationData,Error,Warnings] = ExtractTestCaseData(TestCaseFile,TestCase,OutputType)
.
.
[NumericData,TextData,RawData] = xlsread(TestCaseFile,TestCase);
.
.
%logic to create and populate simulationData structure with data from excel file
.
.
if regularVector
assignin('base',SimulationData.Input(InputIndex).Name,SimulationData.Input(InputIndex).Values(1,:)); %no problem
elseif 2DArray
%now what? I need in the base workspace
%var.time=[TimeValues]
%var.signals.values=[DataValues]
%var.signals.dimensions=[DimValues]
assignin('base',SimulationData.Input(InputIndex).Name,'1');%create signal name with random value, I don't know the value of Name, need to convert to structure form as in the comments
evalin('base','nameIDontKnow.time=SimulationData.Time;'); %two problems actually, referencing a name I don't know in base workspace and base workspace has no concept of what SimulatinData.Time is, and so on if you catch my drift.
.
.
end
Does anyone have an idea of how to make this work?
my solution
for InputIndex
%2D arrays must be in structure form for from workspace blocks (Mathworks)
%make structure in base workspace and populate with values
assignin('base','InputIndex',InputIndex);
assignin('base',SimulationData.Input(InputIndex).Name,'[]');%create the signal/structure name give random value for now
evalin('base', sprintf('%s.time=Time;',SimulationData.Input(InputIndex).Name));
assignin('base','Values',SimulationData.Input(InputIndex).Values);
evalin('base', sprintf('%s.signals.values=Values;',SimulationData.Input(InputIndex).Name));
assignin('base','Dimensions',[size(SimulationData.Input(InputIndex).Values,1) size(SimulationData.Input(InputIndex).Values,2)]);
evalin('base', sprintf('%s.signals.dimensions=Dimensions;',SimulationData.Input(InputIndex).Name));
end
I have a cell array of stucts, each containing the personalia of a person. I put it into this function to get them listed in a text file of a chosen name.
function store( filename, persons )
fid = fopen(filename,'w');
for i=1:length(persons)
fprintf(fid, '%s',serialize_person(persons{i}));
end
Now this function works fine: I enter a <1x3 cell> and get out a text file with three listed persons. However, I want to call this function from another:
function process_store()
list=input('Write in the list of persons you want listed: ');
fprintf('\n')
newfile=input('Give the text file a name: ','s');
store(filename,list)
end
Here I enter the name of the <1x3 cell> as before, but I get a error message "Error using input,Undefined function or variable 'persons'."
Why is this? Am I not using the exact same data as Im using in 'store'?
The problem is that the variable persons isn't accessible inside the function process_store. In Matlab (and most other programming languages) functions can't access variables defined in their calling functions. To understand this better, I recommend having a read of the Wikipedia article on levels of scope.
You essentially have two options here:
Make persons a global variable, both in your workspace and in the function process_store, by using the declaration global persons. I wouldn't recommend this.
Use the function evalin to allow process_store to access variables in its parent workspace.
I'd go with option 2 if I were you. It's a little tricky, so let me explain how it works. Let's create a variable persons in the global workspace.
>> persons = {'John', 'Jack', 'Jill'};
Now say we have the following function
function example()
x = input('Give me a variable name: ');
disp(x)
end
What happens if we try to use it?
>> example()
Give me a variable name: persons
Error using input
Undefined function of variable 'persons'
Error in example (line 2)
x = input('Give me a variable name: ');
Oh dear. That's because the function example doesn't have access to the global workspace, which is where persons is defined. But instead, we can store the name of the variable we want to access, and then check out its value in the global workspace by using evalin, like this
function example()
s = input('Give me a variable name: ', 's');
x = evalin('caller', s);
disp(x)
end
Now if we use it:
>> example()
Give me a variable name: persons
'John' 'Jack' 'Jill'
It works as we expected! Great!
Massive disclaimer
There is almost never a good reason to use functions like evalin (or eval, or assignin or any other function that messes around executing strings as code). There's almost certainly a better way of doing what you want to do. But without knowing what it is you're trying to do, it's hard to give you better advice.
At the prompt
Write in the list of persons you want listed:
if you typed
persons
then you would get exactly that error message if the variable persons was not defined.
I have problem with the following code:
.
.
.
a=zeros(1000,ctimes);
a1=zeros(1000,ctimes);
hold all
for i=num1:num2;
colors=Lines(i);
switch phantom
case 1
path=['E:\filename\'];
path1=['E:\filename2\'];
n=['S',num2str(emt),'_',num2str(i),'.m'];
d=load([path,name]);
a(:,i)=complex(d(:,2),d(:,3)));
n1=['S',num2str(emt),'_',num2str(i),'.m'];
d1=load([path1,name1]);
a1(:,i)=complex(d1(:,2),d1(:,3)));
the problem is that a(:,i) can not be defined. while there is no problem or with complex(d1(:,2),d1(:,3))) , can any expert body help me plz?!
thank you ...
Are you sure you are forming your file name correctly? You are doing something to create a variable n, but using a variable name when you form the path. Here are some recommended debugging steps:
1) make sure the file path is formed correctly:
filePath = fullfile(path, name);
disp(filePath);
The fullfile function concatenates elements of a file path & name, and takes care of using the right file path separator (good for portable code, stops you having to remember to add a / or \ to the end of a file path, etc).
2) check that d is loaded correctly:
clear d;
d = load(filePath);
disp(size(d));
3) check the size of the complex quantity you compute before assigning it to a(:,i):
temp = complex(d(:,2), d(:,3));
disp(size(temp));
By the time you have done these things, you should have found your problem (the dimensions of temp should be [1000 1] to match the size of a(:,i), of course).
As an aside, you should avoid using i as a variable name, especially when you are using complex numbers, since its built-in value is sqrt(-1). Thus, c = a + i * b; would create a complex number (a,b) and put it into c - until you change the meaning of i. A simple solution is to use ii. The same is true for j, by the way. It is one of the unfortunate design decisions in Matlab that you can overwrite built in values like that...
I would like MATLAB to tell me if I have an input file (.m file) that contains some variables with their numbers (i.e., a = 5, b = 6, c = 7) so that I can then use that .m file in another program (main .m file) that uses these variables to calculate S = a + b + c. How can I then read the input file from the main file? Assume the input file is called INP and the main MAIN.
This is typically not good practice in MATLAB. The file containing the input variables would, in your example, be a script. As would your main file. MATLAB does not error when running one script from another, as suggested by ScottieT812, but under certain circumstances strange errors can arise. (Run time compiling has difficulty, variable name collisions across scripts)
A better option is to turn the inputs script into a function which returns the variables of interest
function [a,b c] = inputs
a = 5;
b = 6;
c = 7;
Then this function can be called in the main.m script.
% main.m
[a,b,c] = inputs;
s = a+b+c;
If your "input" file is an m-file, just use the name of the file in your "main" m-file. For example you might have a file called input.m that looks like this:
% File: inputs.m
a = 5;
b = 6;
c = 7;
Then, you can use it in the file main.m like this:
% File: main.m
inputs;
S = a + b + c;
For this sort of stuff (parameters that are easily adjusted later) I almost always use structures:
function S = zark
S.wheels = 24;
S.mpg = 13.2;
S.name = 'magic bus';
S.transfer_fcn = #(x) x+7;
S.K = [1 2; -2 1];
Then you can return lots of data without having to do stuff like [a,b,c,d,e,f]=some_function;
One nice thing about structures is you can address them dynamically:
>> f = 'wheels';
>> S.(f)
ans =
24
It sounds like you want to have some global configuration information that's used by scripts. Often, it's much better to create functions and pass values as arguments, but sometimes it makes sense to do things the way you suggest. One way to accomplish this is to save the information in a file. See "load" and "save" in the Matlab documentation.
I ran into the exact problem KennyMorton mentioned when trying to create runtime compiled versions of MATLAB software for my work. The software uses m-files extensively for passing arguments between functions. Additionally, we create these m-files dynamically which the deployed version of MATLAB does not play nice with. Our workaround was:
save the parameters to a file without the .m extension
read and eval the contents of the file
So, to follow the OPs example, in a function we would create a text file, INP, containing our parameters. We create this file in the directory returned by the ctfroot function. Then, in MAIN, we would use the following to retrieve these parameters:
eval(char(textread(fullfile(ctfroot, INP), '%s', 'whitespace', '');
If the data script is just a script, you can call it from a function or another script directly. Not extra commands required. For example:
%mydata.m
a = 1;
b = 2;
%mymain.m
mydata
whos
mymain
>>mymain
Name Size Bytes Class Attributes
a 1x1 8 double
b 1x1 8 double
This also works for functions in addition to scripts
%foo.m
function foo
mydata
whos
>>foo
Name Size Bytes Class Attributes
a 1x1 8 double
b 1x1 8 double
Generally, it is preferable to use a MAT or other data file for this sort of thing.