Count how many times two numbers occur together

Hi, I am new to matlab and know this is probably an easy thing to program, but I am still learning and am having some trouble.

I have two columns of values and I want to focus on the second column (e.g., [1,1; 1,1; 2,1; 1,0; 2,1] )

The first thing I want to do is count how many times a 1 is preceeded by a 1 (e.g., in the example above there are two occurances where a 1 was preceeded by a 1)

The first row cannot work with this, so I also want to add 1 to the count if the first row is a 1 (in this example the total would actually be 3)

Answer 1

[Image Analyst]

Try this:

m = [1,1; 1,1; 2,1; 1,0; 2,1] 
indexes = strfind(m(:, 2)', [1, 1])
count = length(indexes)

m =

1 1

1 1

2 1

1 0

2 1

indexes =

1 2

count =

2

[Millie Johnston]

This is great! Thank you so much!

I knew it would be easy for someone :)

[Image Analyst]

You're welcome. Could you then please "Accept this answer"? 🙂 Doing so awards answerers "reputation points" and lets others know it's been solved. Thanks in advance.

[Millie Johnston]

Thanks for pointing the reputation points!

I have anothe question similar to the one I have already asked here, so thought I might try ask it in this thread.

How would I calculate the average number of 1s occuring together in the second col?

[Image Analyst]

That's easy with regionprops() - just ask for the Area:

m = [1,1; 1,1; 2,1; 1,0; 2,1] 
indexes = strfind(m(:, 2)', [1, 1])
count = length(indexes)
% Find 1's in second column of m
oneInCol2 = m(:, 2) == 1
% Get the lengths of all the groups of 1's
props = regionprops(oneInCol2, 'Area');
allRegionLengths = [props.Area]
% Get mean of all the lengths
meanRegionLength = mean(allRegionLengths)

You'll see

oneInCol2 =

5×1 logical array

1

1

1

0

1

allRegionLengths =

3 1

meanRegionLength =

2