Finding valid sequences in a list based on specific conditions in matlab

Question

nines 2023-7-19

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评论： nines 2023-7-20

I have a list of scores represented as a cell array in MATLAB, and I need to extract valid sequences from this list based on certain conditions. The scores can be one of three stages: 'Rain', 'Cloud', or 'Sun'.

The conditions for a valid sequence are as follows:

For a sequence of 'Sun' stages, the sequence must have a length of at least 7.

For a sequence of 'Rain' or 'Cloud' stages, the sequence must have a length of at least 7, and all stages within the sequence must be either 'Rain' or 'Cloud'.

I have tried implementing the following code, but it does not provide the correct results for all cases:

scores = {'Rain' 'Cloud' 'Sun' 'Sun' 'Sun' 'Sun' 'Sun' 'Sun' 'Sun' 'Rain'};
sequence_start = 1;
num_scores = numel(scores);
valid_sequences = [];
for j = 1:num_scores
    stage = scores{j};
    
    if strcmp(stage, 'Sun')
        sequence_length = j - sequence_start + 1;
        
        if sequence_length >= 7
            valid_sequences = [valid_sequences; sequence_start, j];
        end
    elseif ismember(stage, {'Cloud', 'Rain', 'Thunder'})
        sequence_length = j;
        
        if sequence_length >= 7 && all(ismember(scores(sequence_start:j), {'Cloud', 'Rain', 'Thunder'}))
            valid_sequences = [valid_sequences; sequence_start, j];
        end
        sequence_start = j + 1;  % Reset sequence_start
    else
        sequence_start = j;  % Reset sequence_start
    end
end
if (num_scores - sequence_start + 1) >= 7
    valid_sequences = [valid_sequences; sequence_start, num_scores];
end

this gives me the results valid_sequences = 3, 9 which is correct (Sun starts at position 3 and ends at position 9).

However, when I put the following test cases in:

test 1:

scores = {'Rain' 'Rain' 'Cloud' 'Cloud' 'Rain' 'Cloud' 'Sun' 'Cloud' 'Rain'};

I get the answer valid_sequences = 9,9

test 2:

scores = {'Sun' 'Rain' 'Cloud' 'Cloud' 'Rain' 'Cloud' 'Rain' 'Cloud' 'Thunder' 'Sun'};

valid_sequences =

7 7

8 8

9 9

Which suggests there seems to be something wrong with how the Rain/Cloud/Thunder gets read in after Sun.

I would be very grateful if you could help!

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Answer 1

Bruno Luong 2023-7-19

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https://ww2.mathworks.cn/matlabcentral/answers/1998073-finding-valid-sequences-in-a-list-based-on-specific-conditions-in-matlab#answer_1275658

编辑：Bruno Luong 2023-7-19

在 MATLAB Online 中打开

See if the results are what you expect (if not please explain why)

getvalidseq({'Rain' 'Cloud' 'Sun' 'Sun' 'Sun' 'Sun' 'Sun' 'Sun' 'Sun' 'Rain'})

ans = 1×2

3 9

getvalidseq({'Rain' 'Rain' 'Cloud' 'Cloud' 'Rain' 'Cloud' 'Sun' 'Cloud' 'Rain'})

ans = 0×2 empty double matrix

getvalidseq({'Sun' 'Rain' 'Cloud' 'Cloud' 'Rain' 'Cloud' 'Rain' 'Cloud' 'Thunder' 'Sun'})

ans = 1×2

2 9

function valid_sequences = getvalidseq(scores)

b = [true; diff(ismember(scores(:), {'Rain' 'Cloud' 'Thunder'})); true];

i = find(b);

n = diff(i);

j = find(n>=7);

valid_sequences = [i(j) i(j+1)-1];

end

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Bruno Luong 2023-7-19

编辑：Bruno Luong 2023-7-19

在 MATLAB Online 中打开

OK this should do it.

getvalidseq({'Rain' 'Cloud' 'Sun' 'Sun' 'Sun' 'Sun' 'Sun' 'Sun' 'Sun' 'Rain'})
ans = 1×2
     3     9
getvalidseq({'Rain' 'Rain' 'Cloud' 'Cloud' 'Rain' 'Cloud' 'Sun' 'Cloud' 'Rain'})
ans = 2×2
     1     6
     8     9
getvalidseq({'Sun' 'Rain' 'Cloud' 'Cloud' 'Rain' 'Cloud' 'Rain' 'Cloud' 'Thunder' 'Sun'})
ans = 1×2
     2     9
function valid_sequences = getvalidseq(scores)
b = [true; diff(ismember(scores(:), {'Rain' 'Cloud' 'Thunder'})); true];
i = find(b);
n = diff(i);
nn = size(n,1);
j1 = (1:2:nn)';
j2 = (2:2:nn)';
jj = {j1, j2};
jj = jj(cellfun(@(j) sum(n(j)), jj) >= 7);
j = cat(1,jj{:});
valid_sequences = [i(j) i(j+1)-1];
end

PS: I reread your original question and you never state the merge thing. I'm notorious here to dislike when people asking incompete question, or change the request during the thread is developping.

nines 2023-7-20

Thank you so so much!!!! I am so sorry for the lack of clarity, I will do better going forward. Thanks so incredibly much, this moves my work forward a ton!!

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