How to group data within a column by specific text within that column

I have a dataset of about 260,000 data points. One of the columns, "species_name'' has various species names within the column. How can I group this data by specific species names (and therefore, group the data in the other columns within the dataset (size, for example) by specific species names)?

[Adam Danz]

Are you just trying to index the table?

load fisheriris
T = table(categorical(species), meas(:,1),meas(:,2),meas(:,3),meas(:,4));
T.Properties.VariableNames{1} = 'Species'

T = 150x5 table
    Species    Var2    Var3    Var4    Var5
    _______    ____    ____    ____    ____

    setosa     5.1     3.5     1.4     0.2 
    setosa     4.9       3     1.4     0.2 
    setosa     4.7     3.2     1.3     0.2 
    setosa     4.6     3.1     1.5     0.2 
    setosa       5     3.6     1.4     0.2 
    setosa     5.4     3.9     1.7     0.4 
    setosa     4.6     3.4     1.4     0.3 
    setosa       5     3.4     1.5     0.2 
    setosa     4.4     2.9     1.4     0.2 
    setosa     4.9     3.1     1.5     0.1 
    setosa     5.4     3.7     1.5     0.2 
    setosa     4.8     3.4     1.6     0.2 
    setosa     4.8       3     1.4     0.1 
    setosa     4.3       3     1.1     0.1 
    setosa     5.8       4     1.2     0.2 
    setosa     5.7     4.4     1.5     0.4 

T(T.Species=='virginica',:)

ans = 50x5 table
     Species     Var2    Var3    Var4    Var5
    _________    ____    ____    ____    ____

    virginica    6.3     3.3       6     2.5 
    virginica    5.8     2.7     5.1     1.9 
    virginica    7.1       3     5.9     2.1 
    virginica    6.3     2.9     5.6     1.8 
    virginica    6.5       3     5.8     2.2 
    virginica    7.6       3     6.6     2.1 
    virginica    4.9     2.5     4.5     1.7 
    virginica    7.3     2.9     6.3     1.8 
    virginica    6.7     2.5     5.8     1.8 
    virginica    7.2     3.6     6.1     2.5 
    virginica    6.5     3.2     5.1       2 
    virginica    6.4     2.7     5.3     1.9 
    virginica    6.8       3     5.5     2.1 
    virginica    5.7     2.5       5       2 
    virginica    5.8     2.8     5.1     2.4 
    virginica    6.4     3.2     5.3     2.3 

[Candice Cooper]

I would accept this answer, but it's a comment. This is essentially what I was trying to do.

ind = find(T.Species=='virginica'), to use your example.

Answer 1

[dpb]

A sample dataset always helps, but probably be good to convert species to a categorical variable first (although not mandatory).

Then using grouping variables -- see

doc findgroups
doc splitapply

if keeping data in an array or look at

doc rowfun

for table, timetable.

[Candice Cooper]

I've tried reading through those and attempting some stuff before posting this question, but I can't seem to figure it out. As an example, I have a column 'species_name' and within that column there is 'star' 'bat' 'crab' randomly dispersed throughout the column. I then have another column of 'size' that corresponds to each of those rows. I'm trying to single out, let's say, 'star' as it's own separate column and the sizes that correspond to those rows in another column.

[dpb]

Well, w/o something to work with, it's harder to guess...attach the table or .mat file with the data, or a short text listing of enough to illustrate.

Then, give us a precise definition of the problem to be solved.

Also, show us what you have tried and where you had a problem.

As I've pointed out in several related Q? recently, rarely do you really need to actually separate out the data into separate arrays; instead of duplicating data already have, use grouping variables and process as wanted.

Answer 2

[dpb]

Illustration with faked data...

tmp=categorical({'star','bat','crab'});     % the categorical variable categories
t=table(tmp(randi(3,[20,1])).',randn(20,1),'VariableNames',{'Species','Size'}); % make up some data
>> head(t)                                  % show what first little bit looks like...
ans =
  8×2 table
    Species      Size  
    _______    ________
     bat       -0.65863
     crab       -1.2834
     crab       0.23872
     bat         1.5475
     star        0.1869
     star       -1.8809
     crab       0.40569
     bat        0.64618
>> summary(t)                           % summary statistics on the table
Variables:
    Species: 20×1 categorical
        Values:
            bat         6    
            crab        9    
            star        5    
    Size: 20×1 double
        Values:
            Min       -1.8809
            Median    0.21281
            Max        1.5967
>> rowfun(@mean,t,'GroupingVariables','Species', ...
                  'InputVariables','Size','OutputVariableNames','GroupMean')  % group means
ans =
  3×3 table
    Species    GroupCount    GroupMean
    _______    __________    _________
     bat           6          0.42427 
     crab          9          0.10477 
     star          5         -0.46693 
>> 

Can do whatever wanted...