How to split a vector in to sub vectors?

I have a vector 'v' of size 8812x1,I want to split it into 20(or known length n) sub-vectors. eg. v = {1,2,3,...,8812}

I wish to see:

v1={1,2,3,...,20}

v2={21,22,23,...,41}

v3 = {42,43,44,...,62}

...

v20 = {...} % the last vector doesn't matter if it can have full 20 or not, it can / might get lesser number as its not fully possible to get a whole 20 elements divide equally with the size of the vector but obviously the vector v1 till v19 must have 20 elements.

Then I want to calculate the median from each sub divided vectors.

So it should be like m1 = median(v1), m2 = median(v2)... m20=median(v20)

I would appreciate if it is done with a loop

[Stephen23]

"I wish to see:"

v1 = {1,2,3,...,20}
v2 = {21,22,23,...,41}
v3 = {42,43,44,...,62}

DO NOT DO THIS.

https://www.mathworks.com/matlabcentral/answers/304528-tutorial-why-variables-should-not-be-named-dynamically-eval

Answer 1

[Stephen23]

Simpler:

>> v = rand(8812,1);
>> b = 20; % block size
>> n = numel(v);
>> c = mat2cell(v,diff([0:b:n-1,n]));
>> z = cellfun(@median,c);

Or if you really want to use a loop, replace the last line with:

z = NaN(numel(c),1);
for k=1:numel(c)
    z(k) = median(c{k});
end

[Md Shahriar Islam]

Hi, I would like to know what to do if block size, b is unknown. That is b is dependent on v.

[Redouane Bouchou]

thank you very much you are a genius

Answer 2

[José-Luis]

v = rand(8812,1);
n = 20;
dummy = nan(20,ceil(numel(v)./n));
dummy(1:numel(v)) = v;
result = nanmedian(dummy)

[Salih Bulut]

This is the fastest code found here.

[Pierre Mathieu]

Yes, very good!

Answer 3

[ES]

v = [1:1:8812];
window_size = 20;
iCount = size(v,2);
iStartIDx = [1:window_size :iCount];
for iLoop=1:length(iStartIDx)-1
    segment{iLoop} = v(iStartIDx(iLoop):iStartIDx(iLoop+1)-1);
    med{iLoop} = median(segment{iLoop});
end
segment{iLoop+1} = v(iStartIDx(iLoop+1):end);
med{iLoop+1} = median(segment{iLoop+1});

[Jayanta Deb]

Thanks Smith. Is something missing at the end of the statement in the second last line after the :? segment(iLoop+1) = v(iStartIDx(iLoop+1):)

[Stephen23]

@J Smith: the code could be improved:

• those output arrays should be preallocated.
• note that square brackets serve no purpose: [1:1:8812] is better written as 1:1:8812 (see the editor warning message and this discussion).
• using median as a variable name is a bad idea.

[José-Luis]

This is rather wrong. On top of being incomplete, as pointed out by Jayanta:

There is no pre-allocation, a performance killer.

median is used both as a variable name and as a function. That's bound to be problematic.

Edit: latest comment was valid before answer being edited.