How do you find data points that match a specific value?

I have a data set (data.tib) that has x, y and z coordinates in columns 1, 2, and 3, respectively. I want to find all unique z values so I used "uz = unique(data.tib(:,3));". For each z-axis position, I want to count how many x-y coordinates there are for each unique z. I was thinking of using "length()" to count how many and then some variation of the "find()" command.

Answer 1

[Cris LaPierre]

I would use groupsummary. If you group by z, the resulting table automatically contains a group count.

x=randi(10,100,1);
y=randi(10,100,1);
z=randi(10,100,1);
data = table(x,y,z);

% group
out = groupsummary(data,'z')

out = 10×2 table
    z     GroupCount
    __    __________

     1         8    
     2         8    
     3        11    
     4         9    
     5        10    
     6        16    
     7        10    
     8        14    
     9         7    
    10         7    

[Talia Vaughn]

I got this error message when I tried to use it "Must specify a method when first argument is a vector or matrix."

[Talia Vaughn]

Nevermind, I fixed that error. Now I'm wondering how to refer to the individual group counts within a line of code.

[Cris LaPierre]

See how to access data in a table. Continuing the example I shared previously, this will access the group count value in the ith row

out.GroupCount(i)