Selecting rows with maximum value with consecutive 3 days occurrence

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Poulomi Ganguli 2017-9-28

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https://ww2.mathworks.cn/matlabcentral/answers/358849-selecting-rows-with-maximum-value-with-consecutive-3-days-occurrence

评论： Jan 2017-9-30

test.mat

I have following matrix in which first, second, third column show year, month, day and value from event 1. However, some of the days are consecutive. I need to choose only those days in a year which contains maximum value in column 3 out of consecutive occurrences.

1 13 0.4659 1970 1 18 29.85
1 14 0.4423 1970 1 18 29.85
1 21 0.5851 1971 1 26 25.63
1 23 0.4701 1971 1 26 25.63
3 18 0.4938 1971 3 19 15.48
2 2 0.4272 1972 2 2 35.33
8 8 0.3888 1972 8 7 7.521
12 27 0.5758 1972 12 28 25.25
12 19 0.5834 1973 12 19 25.97
12 20 0.5414 1973 12 19 25.97
12 23 0.5011 1973 12 19 25.97
1 27 0.4437 1974 1 30 51.96
2 11 0.5594 1974 2 11 45.36
9 2 0.49 1974 9 5 23.04
1 14 0.4255 1975 1 19 17.99
1 15 0.4486 1975 1 19 17.99
9 27 0.381 1975 9 25 5.825
10 11 0.3337 1976 10 14 25.12
12 6 0.3528 1976 11 30 25.93
3 15 0.4784 1977 3 15 15.4
10 8 0.43136 1977 10 6 3.325
12 8 0.4412 1977 12 9 24.1
2 19 0.43 1978 2 25 22.38
2 25 0.4208 1978 2 25 22.38
12 23 0.3763 1978 12 23 24.88
1 3 0.5779 1978 12 28 20.26
2 8 0.4116 1979 2 7 15.01
12 15 0.411 1979 12 15 21.24
3 26 0.47822 1980 3 31 22.5
3 27 0.436 1980 3 31 22.5

The desired output matrix is:

1  13 0.46 1970 1  18 29.85
1  21 0.58 1971 1  26 25.63
3  18 0.49 1971 3  19 15.48
2  2  0.42 1972 2  2  35.33
8  8  0.38 1972 8  7  7.521
12 27 0.57 1972 12 28 25.25
12 19 0.58 1973 12 19 25.97
12 23 0.50 1973 12 19 25.97
1  27 0.44 1974 1  30 51.96
2  11 0.55 1974 2  11 45.36

The associated .mat file is also attached.

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Jan 2017-9-28

在 MATLAB Online 中打开

Please provide the data such, that they can by used by copy&paste. Prefer something like

data = [1 2 3; ...
        4 5 6]

and avoid using commas as decimal separators. Currently all readers have a lot to edit to test their suggestions and this is rather inefficient, because it is enough if this is done once - by yourself.

Poulomi Ganguli 2017-9-28

编辑：Poulomi Ganguli 2017-9-28

Thanks!Then in that case, I'll add a mat file.

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Answer 1

Guillaume 2017-9-28

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https://ww2.mathworks.cn/matlabcentral/answers/358849-selecting-rows-with-maximum-value-with-consecutive-3-days-occurrence#answer_283544

编辑：Guillaume 2017-9-28

在 MATLAB Online 中打开

Finding which days go together:

daygroup = cumsum([1; days(diff(datetime(Z(:, 1:3)))) > 3]);

Then, if you don't want to define a filter function:

[~, grouprow] = splitapply(@max, Z(:, 4), daygroup);
filteredZ = splitapply(@(rows, group) rows(grouprow(group(1)), :), Z, daygroup, daygroup)

If you're happy with a separate filtering function

function rows = filterrows(rows)
   [~, idx] = max(rows(:, 4));
   rows = rows(idx, :);
end

then,

filteredZ = splitapply(@filterrows, Z, daygroup)

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Poulomi Ganguli 2017-9-30

Many thanks! just to be curious rows and group are not MATLAB function, how it's working here?

Jan 2017-9-30

@Poulomi Ganguli: "rows" and "group" are the input variables of the anonymous function provided to splitapply.

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