Classify data (cell array) based on years in MATLAB

Question

Suppose that we have this cell array of data :

a={43 432 2006;
254 12 2008;
65 35 2000;
64 34 2000;
23 23 2006;
64 2 2010;
32 5 2006;
22 2 2010}

Last column of this cell array is years. I want classify data(rows) based on years like this :

a_2006 = {43 432 2006;
32 5 2006;
32 5 2006}

a_2008 = {254 12 2008};

a_2000 = {65 35 2000;
64 34 2000}

a_2010 = {64 2 2010;
22 2 2010}

I have different years in column three in every cell array (this cell array is a sample) so I want an automatic method to determine the years and classify them to a_yearA , a_yearB etc. or other naming that I can distinguish years and call data with years easily in following codes.

How can I do this?

Thanks.da

Answer 1

eval is not recommanded here. I would suggest to save it in a struct array like that

a={43 432 2006;
254 12 2008;
65 35 2000;
64 34 2000;
23 23 2006;
64 2 2010;
32 5 2006;
22 2 2010};

tmp = cell2mat(a);
% clear a or take another variable name for your struct to prevent warnings
clear a 
years=unique(tmp(:,3));
for n = 1:numel(years)
    a.(['a_' num2str(years(n))])=tmp(tmp(:,3)==years(n),:);
end

looks like that

>> a

a = 

    a_2000: [2x3 double]
    a_2006: [3x3 double]
    a_2008: [254 12 2008]
    a_2010: [2x3 double]

>> a.a_2000

ans =

          65          35        2000
          64          34        2000

Furthermore, you can easily access your struct arrays in a loop again (what you can't do such easy with the eval hack).

>> names=fieldnames(a)

names = 

    'a_2000'
    'a_2006'
    'a_2008'
    'a_2010'

>> for n = 1:numel(names)
    a.(names{n})
end

update with strings in cell

Well, say there are strings in your cell

a={'43' '432' 2006;
'254' '12' 2008;
'65' '35' 2000;
'64' '34' 2000;
'23' '23' 2006;
'64' '2' 2010;
'32' '5' 2006;
'22' '2' 2010};

% save original variable 'a' for accessing later
tmp.cell = a;

% save just the years in a matrix for more easy accessing + we need the
% indizes for getting the values from the cell later in the loop
tmp.years = cell2mat(a(:,3));

% clear variable a or take another variable name for your struct to prevent warnings
clear a 

% get unique years for iteration
tmp.unique_years=unique(tmp.years);

for n = 1:numel(tmp.unique_years)
    a.(['a_' num2str(tmp.unique_years(n))])=tmp.cell(tmp.years==tmp.unique_years(n),:);
end

The result is the same, but your structs are now cells

>> a

a = 

    a_2000: {2x3 cell}
    a_2006: {3x3 cell}
    a_2008: {'254'  '12'  [2008]}
    a_2010: {2x3 cell}