Remove for loop and reduce time
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I want to reduce the running time of my code. I found that most of the time in my code is spent in this loop, as this loop is invoked multiple times in my code. Is there anyway to reduce time?? Code explanation: ac1 is an acceleration matrix having values ranging from -10 to 10. I am using discretize function to group different acceleration values into different bins, represented by edges_a. Now, I have to find how many values are there in each bin and store those values in the fourth column of acc_dis matrix.
Here is the code:
if true
edges_a=min(ac1):1.25:max(ac1);
grp_ac=discretize(ac1,edges_a);
for i=1:length(edges_a)
acc_dis(i,4)=sum(grp_ac==i);
end
end
5 个评论
Nithin Banka
2018-6-29
So you want to replace 4th column of 'acc_dis' with the number of times integer 'i' appears in 'grp_ac'?
Nagesh A P
2018-6-29
Nithin Banka
2018-6-29
Then, what I though of is, instead of calling sum() in every loop iteration, since 'i' cannot be beyond the length 17. So we define a temporary array with the length of 'i' and then run a loop through 'grp_ac' and increment the temporary array element according to the number. That way we just need to run through all the elements in grp_ac once to get the required answer. I hope this will take less time.
I know this is not so clear. Can you tell me the size of 'grp_ac'? I will try reproducing what I told you and post you the code if I get good results.
Nagesh A P
2018-6-29
Jan
2018-6-29
@Nagesh A P: Please post a relevant set for the input data.
采纳的回答
Guillaume
2018-6-29
Points for using discretize instead of writing your own loop for that. The thing is, what you really want is the histogram and there's also a function for that: histcounts:
edges_a = min(ac1):1.25:max(ac1);
h = histcounts(ac1, edges_a);
acc_dis(1:numel(h), 4) = h;
Note: I don't know how many rows acc_dis has. Hopefully at least enough. If it already has the correct number of rows, that last line can be simplified to:
acc_dis(:, 4) = h;
Note 2: If you still need grp_ac, then:
[h, ~, grp_ac] = histcounts(ac1, edges_a);
更多回答（1 个）
Nithin Banka
2018-6-29
编辑：Nithin Banka
2018-6-29
if true
edges_a=min(ac1):1.25:max(ac1);
grp_ac=discretize(ac1,edges_a);
len = length(edges_a);
auxArr = zeros(len, 1));
len1 = length(grp_ac);
for i=1:len1
if(grp_ac(i)<=len&grp_ac(i)>=1)
auxArr(grp_ac(i)) = auxArr(grp_ac(i)) + 1;
end
end
acc_dis(1:len, 4) = auxArr;
end
I think this should help.
3 个评论
Nagesh A P
2018-6-29
Nithin Banka
2018-6-29
The code you used runs through grp_ac in every iteration in the 'grp_ac==i' command. That will make it kind of for loop inside a for loop.
Nagesh A P
2018-6-29
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