Comparing 2 columns of a matrix

I want to compare 2 columns of my matrix as shown below:

For example, I have the number 4 in the first column occurring thrice. I need to compare it's corresponding values in column 2 and obtain the minimum value among them. I then need to store that value in another matrix.

Could someone suggest me a way to get this desired result.

Thanks and regards

Answer 1

[Star Strider]

Try this (using the accumarray (link) function):

A = [randi(10, 20, 1) rand(20,1)]                               % Create Data
[A1u,~,idx] = unique(A(:,1));                                   % Unique Values & Indices
MinVals = accumarray(idx, A(:,2), [], @(x)min(x));              % Find Minimum Of Each
Result = [A1u, MinVals]                                         % Desired Result

Use your own matrix for ‘A’.

[Gautami Golani]

Hey,

Thank you so much for this.

It helped me get what I was looking for.

Could you just explain the basic idea behind the code?

It would be helpful for me in the future if i face a similar problem.

Thanks and regards

[Star Strider]

As always, my pleasure.

The unique call outputs the unique elements in the first column as ‘A1u’ here, and the row indices they are associated with in ‘idx’. The accumarray call accumulates the values in the second column that are identified with each ‘idx’ value, and then calculates the minimum of them and outputs it in ‘MinVals’. The ‘Result’ matrix then simply presents the unique values in the first column and the minimum of each in the second column.

[Gautami Golani]

Thanks a lot for the explanation.

[Star Strider]

As always, my pleasure.

Answer 2

[Image Analyst]

You can do this easily with unique() and histogram() or histcounts(). Since you didn't include your data in a way that's easy for us to code up, I assume you'd prefer to do it yourself, so give it a try. If you run into problems, attach your data and explain the problem(s).

[Gautami Golani]

My code is as shown below. It's just a part of my entire program.

I'm trying to compare all the 3 values of the number 4.0000 in column 2 and find out the min of them.

Example: For 4.000 the corresponding values in column 2 are 0.0042, 0.0028 and 0.0015.

So my new matrix should have the min of these 3, which is 0.0015.

Thanks