How to attribute a letter to unique combinaisons

Hi,

I have a very simple question that is a bit tricky to explain: I have a table like this

var_a = {'T1','T1','T1','T1','T1','T1','T2','T2','T2','T2','T2','T2','T2','T2'}';
var_b = [2,2,2,2,3,3,8,8,8,9,9,10,10,11]';
t = table(var_a, var_b)

and for every unique var_a id, I want every unique combinaison between var_a and var_b to be attributed a different letter beginning with 'A'. In other words the desired output would looks like this:

var_a = {'T1','T1','T1','T1','T1','T1','T2','T2','T2','T2','T2','T2','T2','T2'}';
var_b = [2,2,2,2,3,3,8,8,8,9,9,10,10,11]';
var_c = {'A', 'A', 'A', 'A', 'B', 'B', 'A', 'A', 'A', 'B', 'B', 'C', 'C', 'D'}';
desired_out_put = table(var_a, var_b, var_c)

Thank you,

Answer 1

[Stephen Cobeldick]

There does not seem to be a convenient way to apply a function to table groups that does not also accumulate the results (e.g. like splitapply does). Here is one workaround:

>> A = {'T1';'T1';'T1';'T1';'T1';'T1';'T2';'T2';'T2';'T2';'T2';'T2';'T2';'T2'};
>> B = [2;2;2;2;3;3;8;8;8;9;9;10;10;11];
>> T = table(A,B)
T = 
     A      B 
    ____    __
    'T1'     2
    'T1'     2
    'T1'     2
    'T1'     2
    'T1'     3
    'T1'     3
    'T2'     8
    'T2'     8
    'T2'     8
    'T2'     9
    'T2'     9
    'T2'    10
    'T2'    10
    'T2'    11
>> G = findgroups(T.A);
>> F = @(b) {num2cell(char('A'+cumsum([0;diff(b)~=0])))};
>> Y = splitapply(F,T.B,G);
>> T.C = cell(height(T),1); % preallocate
>> for k = 1:max(G), T{G==k,'C'} = Y{k}; end
>> T
T = 
     A      B      C 
    ____    __    ___
    'T1'     2    'A'
    'T1'     2    'A'
    'T1'     2    'A'
    'T1'     2    'A'
    'T1'     3    'B'
    'T1'     3    'B'
    'T2'     8    'A'
    'T2'     8    'A'
    'T2'     8    'A'
    'T2'     9    'B'
    'T2'     9    'B'
    'T2'    10    'C'
    'T2'    10    'C'
    'T2'    11    'D'

[012786534]

Neat answer. Thank you.