Add particular elements of array

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Awais Saeed
Awais Saeed 2021-8-1
评论： Rik 2021-8-1
Let's say that k is a vector and
k = [1 1 1 1 4 1 1];
k could be anything I just assumed [1 1 1 1 4 1 1]. Let's say there is a variable
limiter = 3;
I want to add elements of k that are less than or equal to the variable 'limiter' and put it in a new vector, let's say k_new. For example, k(1),k(2),k(3),k(4) <= limiter, add them and put it in k_new resulting
k_new = [4];
Now k(5) is greater than limiter, it should be ignored and should be stored in k_new as it is, resulting
k_new = [4 4];
the final desired vector is
k_new = [4 4 2]
I worte a program using two while loops and somehow the loop keeps running. I want to do this using a single while loop if possible and I need help in doing that. Below is my code
limiter = 3;
k = [1 1 1 1 4 1 1];
run1 = true;
while (run1)
ii = 1;
jj = 1;
run2 = true;
while (run2)
if (k(ii) < limiter)
k_new(jj) = k(ii)+k(ii+1)
ii = ii + 2; % increment of 2 because we need
% to check k(ii+2) as k(ii) and k(ii+1) have been checked
else
k_new(jj) = k(ii)
ii = ii + 1;
end
jj = jj + 1;
if (ii == length(k))
k_new(jj) = k(ii)
break
end
if (ii > length(k))
run2 = false;
end
end
k = k_new
clear k_new
if (find(k==min(k),1,'last') == length(3)) % Stop the outer while loop
run1 = false;
break
end
end

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采纳的回答

Rik
Rik 2021-8-1
Ran in:
Not the tidiest code, but it all happens in a single loop, with cumsum doing the addition prior to the loop.
%set your data
data=[1 1 1 1 4 1 1];
limiter=3;
%add all elements together
c1=cumsum(data);c2=NaN(size(c1));
%c1 will hold the corrected cummulative sums (masked with -inf)
%c2 will contain the end result (masked with NaNs)
while true
ind=find(c1>limiter,1);
if isempty(ind)
%break loop
if isnan(c2(end)),c2(end)=c1(end);end
[c1;c2]
break
end
c1((ind+1):end)=c1((ind+1):end)-c1(ind);
c2(ind)=c1(ind);
c1(1:ind)=-inf;
[c1;c2]
end
ans = 2×7
-Inf -Inf -Inf -Inf 4 5 6 NaN NaN NaN 4 NaN NaN NaN
ans = 2×7
-Inf -Inf -Inf -Inf -Inf 1 2 NaN NaN NaN 4 4 NaN NaN
ans = 2×7
-Inf -Inf -Inf -Inf -Inf 1 2 NaN NaN NaN 4 4 NaN 2
k_new=c2(~isnan(c2))
k_new = 1×3
4 4 2
  2 个评论
Awais Saeed
Awais Saeed 2021-8-1
Hey @Rik, It worked brilliantly and that's a very good way of using cumsum. Thank you very much. Just wondering if we can add elements which are >= limiter instead of <= limiter? I might need to do this in future.
Rik
Rik 2021-8-1
I don't think I completely understand what you mean, but it probably would not be too hard to modify this code. I would encourage you to try it yourself.

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