提高MATLAB代码速度

Question

一些指示,将不胜感激.我正在阅读大约1M行数据,使用以下代码需要大约24小时.如何改善执行时间？

该阵列Day包含n的值^第一天从一开始和有特定日期更然后一个记录.该程序检查特定ID(存储在unique_id)是否在180天内重复.

%// calculating the number of repeats within 180 days
fid2 = 'data_050913/Unique_id_repeat_count1.xlsx';
fid1 = 'data_050913/data_050913_2000.csv';

fid_data = fopen(fid1);
data     = fgetl(fid_data); %// the first line, title line
ep       = 0; %// position point number

while 1
    data = fgetl(fid_data);
    if(length(data)<10)
      break;
    end
    ep = ep+1;
    id = find(data == ',');
    unique_id(ep) = str2num(data(1:id(1)-1)); 
    day(ep) = str2num(data(id(8)+1:id(9)-1)); 
end

repeat = zeros(ep,1);

tic
i = 1; 
count = 0;
while i <= ep
    j = i+1;
    while ( (j<=ep) && (day(j)<= day(i)+179) )
        if unique_id(i) == unique_id(j)
           count = 1;
           break;
        end
        j = j+1;
    end

    repeat(i,1) = count;

    count = 0;
    i = i+1;
end
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i = 1;
k = 1;
while i<=ep
    count = repeat(i,1);
    j=i;
    while (day(j) == day(i))
        count = repeat(j,1)+count;
        j = j+1;
        if j > ep
            break;
        end
    end

    day_final(k,1)= day(i);
    repeat_final(k,1) = count;

    k = k+1;
    i = j;
end

xlswrite(fid2,day_final,'Repeat_Count','A2');
xlswrite(fid2,repeat_final,'Repeat_Count','B2');

谢谢

Answer 1

下面的代码运行速度比原始代码快约 200 倍，并给出相同的结果。

当然，加速取决于输入数据的分布，我的假设可能不正确（我有 1000 个唯一 ID，平均每天 19 条记录）。

我还编写了一些代码来生成与我认为您的输入数据类似的数据。

% Generate Input data 
ep = 100000;

isRepeatedDay = rand(1,ep) < 0.95;
day = cumsum(~isRepeatedDay);
unique_ids = 1:1000;
unique_id_indices = round(rand(ep,1)*length(unique_ids));
unique_id_indices(unique_id_indices < 1) = 1;
unique_id_indices(unique_id_indices > length(unique_id_indices) ) = length(unique_id_indices);

unique_id = unique_ids(unique_id_indices);

%Process the input data to find repeats
tic
repeat = zeros(ep,1);
[unique_values,~,indices] = unique(unique_id);
for uv_index = 1:length(unique_values)
    uv = unique_values(uv_index);
    uv_indices = find(indices == uv_index);
    for i=1:length(uv_indices)-1
        daysDifference = day(uv_indices(i+1)) - day(uv_indices(i));
        if daysDifference <= 179
            repeat(uv_indices(i),1) = 1;
        end
    end
end
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