Comparing data in a matrix/table

In the table above, focus on the elements of columns 3 and 4. Column 3 is the object number and Column 4 is its "group." I want to count how many times an object was grouped in both 1 and 2. Store it in a variable "count." The value of "count" based on the table above should be 2 because only object numbers 11 and 17 were grouped in both 1 and 2.

EDIT: To make indexing easier, the name of the table above shall be called TableA

[Ive J]

This looks like a homework to me. What have you tried so far?

[Joaquin Lalusin]

Its not homework per se, more of a personal project.I have already processed the data I'm working with to result in the table above. I'm currently trying to index my data to figure out how many "objects" each "group" share. I've been racking my brain around for hours but haven't had any luck. I've been thinking of making a nested for and if loop but I cant think of the best way how.

Answer 1

[Ive J]

One way would be to use groupsummary:

tab = 
       a1          a2       a3    a4
    ________    ________    __    __

     0.84913    0.046171    10    1 
     0.93399    0.097132    10    1 
     0.67874     0.82346    11    1 
     0.75774     0.69483    11    2 
     0.74313      0.3171    12    1 
     0.39223     0.95022    14    1 
     0.65548    0.034446    14    1 
     0.17119     0.43874    14    1 
     0.70605     0.38156    14    1 
    0.031833     0.76552    17    2 
     0.27692      0.7952    17    1 

G = groupsummary(tab, {'a3','a4'})

    a3    a4    GroupCount
    __    __    __________

    10    1         2     
    11    1         1     
    11    2         1     
    12    1         1     
    14    1         4     
    17    1         1     
    17    2         1  
 

So, number of repeats in column a3 would the variable count:

[a3unique, ~, idx] = unique(G.a3, 'stable');
count = histcounts(idx, [1:numel(a3unique), inf]);
count
    1     2     1     1     2
    
 a3unique'
    10    11    12    14    17

[Joaquin Lalusin]

Thank you for your time! This isn't quite what I was aiming for but you gave me a pretty good idea of what to do anyways so thank you so much!