How about the following?
% Example of the input array
Act = repmat({'Dive';'Run';'Walk'},4,1);
uniqueAct = unique(Act);
Count = nan(size(Act));
for kk = 1:numel(uniqueAct)
idx = strcmp(Act,uniqueAct{kk});
Count(idx) = 1:nnz(idx);
end
T = table(Act,Count);
>> T
T =
12×2 table
Act Count
________ _____
{'Dive'} 1
{'Run' } 1
{'Walk'} 1
{'Dive'} 2
{'Run' } 2
{'Walk'} 2
{'Dive'} 3
{'Run' } 3
{'Walk'} 3
{'Dive'} 4
{'Run' } 4
{'Walk'} 4
