根据条件语句Matlab对列的部分求和

Question

我在 matlab 中有一个矩阵，如果其他列使用条件语句检查，我想对列的值求和，然后我想以连贯的方式存储求和值。

布局输入table ListMax:

year    Month    day    hour    precipitation  
1998    1        1      1       5
1998    1        2      2       7
1998    1        3      3       0
....    ...     ...    ...      ...

布局输出result_matrix:

year    jan    feb   mar    
1998    100    120   140
1999    90     110   130
...    ...     ...   ...

我正在努力处理遍历行、检查条件语句和将值保存在输出中的组合。

我有以下想法，但没有用：

result_matrix = zeros(15,12);   %empty matrix 15 years, 12 months
year_number = 1998;
counting_years = 1;
counting_months = 1; 

for (ii = 1: length(ListMax));
    if ListMax(:,1) == year_number && ListMax(:,2) == counting_months;
        result_matrix(counting_years, counting_months) = (sum(Listmax(:,5));
    else % update month itirators
        if counting_months < 12
            counting_months = counting_months + 1;
        else % end of year, set month count to 1
            counting_months = 1;
        end
     year_number = year_number +1;
     counting_years = counting_years + 1;
     end
end

我知道这可能不是最直接的方法，但目前这是我能想到的方法，现在我只需要让它工作。任何朝着正确方向的推动将不胜感激:)

Answer 1

这个怎么样（未测试）：

year_start = 1998;
year_end = 2016;
result_matrix = zeros(year_end-year_start+1,12);

for year = year_start:year_end
    for month = 1:12
        rows = (ListMax(:,1)==year) & (ListMax(:,2)==month);
        result_matrix(year-year_start+1,month) = sum(ListMax(find(rows),5));
    end
end

Answer 2

您可以简单地使用带有两列子索引的 accumarray。

year    Month    day    hour    precipitation  
1998    1        1      1       5
1998    1        2      2       7
1998    1        3      3       0
....    ...     ...    ...      ...

例如，如果你想根据年份和月份求和总降水量，你可以使用矩阵的第一列作为索引，最后一列作为降水量的值。

sub = 1998    1     %Jan.1998  
      1998    1     %Jan.1998   
      1998    2     %Feb.1998 
      ...
sub(:,1) = sub(:,1) - (min(sub(:,1))-1); %so the index for the year start at 1 and not 1998.

val = 6 %millimeter of precipitation on Jan.1998 day xxx
      4 %millimeter of precipitation on Jan.1998 day xxx
      7 %millimeter of precipitation on Feb.1998 day xxx
      ....

现在使用 accumarray:

result = accumarray(sub,val,[],@sum);

根据条件语句Matlab对列的部分求和

Sum parts of column depending on conditional statement Matlab

matlab

conditional

sum

matrix