MATLAB: The “unique” function returns “Index exceeds matrix dimensions” error

index exceeds matrix dimensionsunique function

I have a .mat file loaded in the Workspace. I execute the command

unique = unique(datafile.data(:,2));

It creates the unique array successfully. When I execute the very same command for a second time, what should happen? The array 'unique' should be created again and the one in the Workspace should be replaced. No, instead, I get the error 'Index exceeds matrix dimensions.' If I assign the statement to a different name like

a = unique(datafile.data(:,2));

I get the same error. So the first time I execute the command, no problem. The second time I execute it, I get the error. What is going on?

Best Answer

I'm pretty sure that what is happening is that the first time, you have defined the variable called unique, which is a bad idea because it is the same name as the function.

The second time through that code, MATLAB is trying to access the variable, not the function, so you get the error.

The fact that you get the error again when assigning the output to a suggests to me that you still have the variable named unique in the workspace. Clear that variable out and try again.

Related Solutions

MATLAB: Does the code not work correctly if I use the EVAL, ASSIGNIN or LOAD function to create a workspace variable that has the same name as a MATLAB function

This is a limitation of MATLAB when the EVAL function (and related functions such as ASSIGNIN, LOAD) is used to create workspace variables that have the same name as a MATLAB function. The MATLAB Interpreter attempts to determine if an identifier represents a function name at parse time, and if so, binds to that function. This allows for a substantial performance improvement, but introduces some limitations. Because the MATLAB Interpreter cannot determine what variables an EVAL statement will create, it ends up binding "sum" to the SUM function in the example below:

function test
a = 1;
b = 2;
c = 3;
names = {'a','b','c'};
for idx = 1:length(names)
     eval(['sum.', names{idx}, '=', names{idx}, ';'])
end
exist('sum')
sum

One way to work around this limitation is to move the assignment outside of the EVAL function. For example:

function test
a = 1;
b = 2;
c = 3;
names = {'a','b','c'};
for idx = 1:length(names)
     sum.(names{idx}) = eval(names{idx});
end
exist('sum')
sum

Another workaround is to initialize the variable at the onset:

function test
a = 1;
b = 2;
c = 3;
sum = 0;
names = {'a','b','c'};
for idx = 1:length(names)
     eval(['sum.', names{idx}, '=', names{idx}, ';'])
end
exist('sum')
sum

MATLAB: Logical Indexing

idx = a(:,2) > 1;
a   = a(idx,:)

with a(idx) - note no ,: - you're saying to take the elements indexed by idx.

with a(idx,:) you're saying to take the rows indexed by idx.

Best Answer

Related Solutions

MATLAB: Does the code not work correctly if I use the EVAL, ASSIGNIN or LOAD function to create a workspace variable that has the same name as a MATLAB function

MATLAB: Logical Indexing

Related Question