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Getting cetral weighted value in an Array

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Sajid Khan
Sajid Khan 2013-8-13
Hi there,
Suppose I have an Array
a = [0 0 1 1 1 2 3 5 6 7 7 99 100]
It's median value is 3 for sure, but center weighted value is 5 as if we assign weights to the array, then the weight matrix become
weight_a = [1 1 2 2 2 3 4 5 6 7 7 8 9]
whose center weight is 5. Is there any efficient way in Matlab to find the center weight? one way is to use unique function which discards duplicate values and give you an array with unique element, from that unique array, median value is the center weighted. But unique function is time consuming if you apply tic toc to it.
So is there any other way to find center weighted element.

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回答（1 个）

Andrei Bobrov
Andrei Bobrov 2013-8-13
编辑：Andrei Bobrov 2013-8-14
a1 = sort(a(:));
out = median(a1([true;diff(a1)~=0]));
ADD
a1 = sort(a(:));
ii = find([true;diff(a1)~=0]);
i2 = ceil(numel(ii)/2);
out = a1(ii(i2));
or
i1 = unique(a);
out = i1(ceil(numel(i1)/2));
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Sajid Khan
Sajid Khan 2013-8-13
I think it's problem with median function that if I try to find median of following variable a = [ 0 164 165 166 167 168 170 171 172 173 174 255], it give me wrong value

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