Efficient way to fill vector values from another vector
显示 更早的评论
Hi,
Sorry for a similar topic to my last question, but I am finding it difficult to think outside loops.
Given 2 vectors, one signal and one values, I would like to produce a 3rd output vector which replaces the zeros of the signal input with the value of the previous corresponding 1.
For example in the sample inputs below, the first two 0's are given with 45, which is the value corresponding to the first 1 after these zeros. Each 1 will have it's corresponding value
inputSignal = [1;0;0;1;1;1;0;1]; inputTargets = [34;46;54;45;34;22;12;34]; retTargets = [34;45;45;45;34;22;34;34];
I have made various attempts and the following is the fastest I can get it over large input vectors. I got the strfind function from a previous post, but I cannot find a way to do the fill without the for loop. It works fine, but I am wondering if there is a neater vectorized way. I have used find() in a loop but this is very slow.
inputSignal = [1;0;0;1;1;1;0;1];
inputTargets = [34;46;54;45;34;22;12;34];
rollingTargets = flipud(inputTargets);
rollingTargets1 = rollingTargets;
retTargets = rollingTargets;
%Find the 1's
a = strfind([flipud(inputSignal)' 0], [1 0]);
b = a(2:end);
%Fill the zeros
for i=1:size(b, 2)
rollingTargets(a(i):b(i)) = rollingTargets1(a(i));
end
rollingTargets(a(i+1):end) = rollingTargets1(a(end));
%fill the 1's
retTargets = flipud(rollingTargets);
c = find(inputSignal);
retTargets(c) = inputTargets(c);
采纳的回答
Teja Muppirala
2011-4-19
Sometimes the answer is simpler than you think:
retTargets = inputSignal.*inputTargets;
for n = numel(retTargets)-1:-1:1
if retTargets(n) == 0
retTargets(n) = retTargets(n+1);
end
end
3 个评论
Oleg Komarov
2011-4-19
Nice +1
RoJo
2011-4-20
Oleg Komarov
2011-4-20
If you preallocate properly (as done here), loops can be faster in many cases.
更多回答（2 个）
Andrei Bobrov
2011-4-19
old variant
p=flipud(inputSignal);
p1 = flipud(inputTargets);
ne = diff(find(diff([~p(1); p(:); ~p(end)]))); %idea by Walter Roberson
np = length(p);
I = (1:np).';
Ifirst = I([true; diff(p)~=0]); % idea by Matt Fig
z = p(Ifirst)==0;
if z(1) , z(1)=0; end
Nums = p1(Ifirst(z)-1);
Cns = mat2cell(I,ne,1);
p1(cat(1,Cns{z}) ) = cell2mat(cellfun(@(x,y)x*ones(y,1),num2cell(Nums),num2cell(ne(z)), 'UniformOutput', false));
outTargets = reshape(flipud(p1),size(inputTargets));
Oleg Komarov
2011-4-19
tic
[len,val] = rude(inputSignal);
newval(inputSignal == 1) = find(inputSignal);
cumlen = cumsum(len)+1;
idx = ~val;
newval(inputSignal == 0) = rude(len(idx),cumlen(idx));
retTargets = inputTargets(newval);
toc
tic
retTargets(logical(inputSignal)) = inputTargets(logical(inputSignal));
[len, val] = rude(retTargets);
idx = val == 0;
val(idx) = val(find(idx) + 1);
retTargets = rude(len,val);
toc
类别
在 帮助中心 和 File Exchange 中查找有关 Loops and Conditional Statements 的更多信息
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!
Translated by 
