Matlab：优化此（第 2 部分）

Question

这是另一个：

ValidFirings = ((DwellTimes > 30/(24*60*60)) | (GroupCount > 1));

for i = length(ValidFirings):-1:2
    if(~ValidFirings(i))
        DwellTimes(i-1) = DwellTimes(i)+DwellTimes(i-1);
        GroupCount(i-1) = GroupCount(i)+GroupCount(i-1);
        DwellTimes(i) = [];
        GroupCount(i) = [];
        ReducedWallTime(i) = [];
        ReducedWallId(i) = [];
    end
end

似乎目的是根据传感器触发是否被认为有效来总结“停留时间”。因此，我有一个传感器触发向量，如果当前行未标记为有效，我将向后遍历并汇总到前一行。

我可以在 C/C++ 中将其可视化，但我不知道如何将其转换为更好的 Matlab 向量表示法。就目前情况而言，这个循环非常慢。

编辑： 我可以使用某种形式的 DwellTimes = DwellTimes( cumsum( ValidFirings )) 吗？

Answer 1

与您之前的问题一样，替换 for 循环应该可以提高性能。

%# Find the indices for invalid firings
idx = find(~(DwellTimes > 30/(24*60*60)) | (GroupCount > 1));

%# Index the appropriate elements and add them (start the addition
%# from the second element)
%# This eliminates the for loop
DwellTimes(idx(2:end)-1) = DwellTimes(idx(2:end)-1)+DwellTimes(idx(2:end));
GroupCount(idx(2:end)-1) = GroupCount(idx(2:end)-1)+GroupCount(idx(2:end));

%# Now remove all the unwanted elements (this removes the 
%# first element if it was a bad firing.  Modify as necessary)
GroupCount(idx)=[];
DwellTimes(idx)=[];

Answer 2

我会先如图所示进行合并，然后消除无效数据。这避免了不断调整数据大小。请注意，由于值传播的方式，您无法颠倒 FOR 循环的顺序。

ValidFirings = ((DwellTimes > 30/(24*60*60)) | (GroupCount > 1));

for i = length(ValidFirings):-1:2
    if (~ValidFirings(i))
        DwellTimes(i-1) = DwellTimes(i) + DwellTimes(i-1);
        GroupCount(i-1) = GroupCount(i) + GroupCount(i-1);
    end
end

DwellTimes      = DwellTimes(ValidFirings);
GroupCount      = GroupCount(ValidFirings);
ReducedWallTime = ReducedWallTime(ValidFirings);
ReducedWallId   = ReducedWallId(ValidFirings);