Is it possible to add an element to a "sub array"?

Im not sure what the proper term for this structure is in Matlab, but I have the following variable

stateMeasurements = {[] [] [] [] []};

Every array is supposed to contain basically a pair of start time and end time, so if I want to add a measurement for State 1 for example, I would like to do something like this

stateMeasurements(1).push([5, 10]);

I can first get the sub array and add the measurement to it, but then I can put it back into stateMeasurements.

m = stateMeasurements(1);
m{end+1}=[5, 10];
stateMeasurements(1) = m % This gives an error

The error I receive is "Unable to perform assignment because the left and right sides have a different number of elements."

I know how to achieve this in other programming languages but how can I do this in Matlab?

Answer 1

[Kunal Kandhari]

Hello Vincent,

For an existing cell array stateMeasurements, you can assign a new element to the end using direct indexing. For example

stateMeasurements{6}=[10,11]

or

stateMeasurements{end+1}=[20,26]

where "end" is a special keyword in MATLAB that means the last index in the array. So in your specific case of n elements, it would automatically know that "end" is your "n".

Another way to add an element to a "cell array" is by using concatenation:

stateMeasurements=[stateMeasurements,[10,22]];

For more information, see below documentations:

• Cell Arrays
• Add Cells to Cell Array

[Vincent]

This would create a structure like this

{[] [] [] [] [] [20, 26]}

What I am trying to accomplish is adding items to the sub arrays.

So like this:

{[] [] [[20, 26]] [] []}

So the main stateMeasurements should only have 5 elements, but I want to extend the elements themselves.

Is that possible?

[Jan]

@Vincent: [] is Matlab's operator for the concatenation. "[ ]" is used to display an empty array, but of course there are no brackets anywhere. |[[20,26]] is exactly the same as [20, 26].

To obatin the wanted output:

stateMeasurements = {[] [] [] [] []};
stateMeasurements{3} = [20, 26];

Note the curly braces for the cell indexing. The same result, but slightly slower in the execution:

stateMeasurements(3) = {[20, 26]};

Now the right side creates a scalar cell array and inserts in as 3rd element of stateMeasurements. It is faster to insert the contents directly as shown above.

If you want to attach further values to this vector:

stateMeasurements{3} = [stateMeasurements{3}; [1, 2]];

Now the 3rd element of the cell vector stateMeasurements contains the matrix [20, 26; 1, 2].

[Vincent]

That works! Thank you Jan