How to keep the previous iteration in a for loop?

Question

Michiel Smit 2020-6-6

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/543431-how-to-keep-the-previous-iteration-in-a-for-loop

评论： Michiel Smit 2020-6-6

Dear Reader,

I am trying to use a for loop to find the maximum daily value for water level (WL) for a hourly data set between the years 2000 and 2020. The code has been specifically written to also take shorter months (february) in to account. See below.

I want the line WL_HVH_dailymax_total a matrix keeping the [year month day WL], for example

[2000 01 01 WL; 2000 01 02 120 WL; 2000 01 03 WL ]

However, the way I have written this, it will overwrite the previous line so that the only result I obtain is:

[2020 06 05 125]

DO I need an extra line of code, or what other way can I fix this?

for i = 2000:max(WL_HVH(:,1));
    WL_HVH_year = WL_HVH(WL_HVH(:,1)==i, :);
    for j = 1:max(WL_HVH_year(:,2));
        WL_HVH_month = WL_HVH_year(WL_HVH_year(:,2)==j, :);
        for k = 1:max(WL_HVH_month(:,3));
            WL_HVH_day = WL_HVH_month(WL_HVH_month(:,3)==k, :);
            WL_HVH_dailymax = max(WL_HVH_day(:,6));
            WL_HVH_dailymax_total = [i j k WL_HVH_dailymax];
        end
    end
end

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Answer 1

David Hill 2020-6-6

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https://ww2.mathworks.cn/matlabcentral/answers/543431-how-to-keep-the-previous-iteration-in-a-for-loop#answer_447242

在 MATLAB Online 中打开

count=1;
for i = 2000:max(WL_HVH(:,1));
    WL_HVH_year = WL_HVH(WL_HVH(:,1)==i, :);
    for j = 1:max(WL_HVH_year(:,2));
        WL_HVH_month = WL_HVH_year(WL_HVH_year(:,2)==j, :);
        for k = 1:max(WL_HVH_month(:,3));
            WL_HVH_day = WL_HVH_month(WL_HVH_month(:,3)==k, :);
            WL_HVH_dailymax = max(WL_HVH_day(:,6));
            WL_HVH_dailymax_total{count} = [i j k WL_HVH_dailymax];%make cell array
            count=count+1;
        end
    end
end

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David Hill 2020-6-6

在 MATLAB Online 中打开

count=1;
for i = 2000:max(WL_HVH(:,1));
    WL_HVH_year = WL_HVH(WL_HVH(:,1)==i, :);
    for j = 1:max(WL_HVH_year(:,2));
        WL_HVH_month = WL_HVH_year(WL_HVH_year(:,2)==j, :);
        for k = 1:max(WL_HVH_month(:,3));
            WL_HVH_day = WL_HVH_month(WL_HVH_month(:,3)==k, :);
            WL_HVH_dailymax = max(WL_HVH_day(:,6));
            WL_HVH_dailymax_total(count,:) = [i j k WL_HVH_dailymax];%change to matrix
            count=count+1;
        end
    end
end