Reduce the number of zeros in an array

Hello,

Please help me with the following:

I study some data that contain arrays with many repeated zeros.

I need to reduce the number of zeros by a certain number.

For example,

Consider the array

A=[1.140,0.590,0.140,0,0,0,0,0,0,0,0,0,0,0,0,1,3,5];

How can I reduce the number of zeros 3 times?

The number of zeros in A is 12 and I want to keep only 4.

The final array would be

B=[1.140,0.590,0.140,0,0,0,0,1,3,5];

Thank you.

Pavlos

Answer 1

[Jorrit Montijn]

Hi Pavlos,

I'm not sure what the purpose would be of reducing the number of zeros, but here's one way to do it by removing one randomly selected third of all zeros:

% First, define the vector:
A=[1.140,0.590,0.140,0,0,0,0,0,0,0,0,0,0,0,0,1,3,5];

% then search for the locations where the vector has zeros:
vecZeroLocations=find(A==0);

% count how many zeros there are:
intNumZeros=numel(vecZeroLocations);

% select one third of zeros to remove:
vecRemoveZeros = randperm(intNumZeros,round(intNumZeros/3));

% now we have to get the locations in the original vector of those zeros:
vecRemoveLocations = vecZeroLocations(vecRemoveZeros);

% and finally, we can remove those zeros from the vector:
A(vecRemoveLocations)=[];

I hope this answers your questions?

Best, Jorrit

[Jorrit Montijn]

I just realized you wanted to throw away 2/3 of the zeros. In this case, use:

vecRemoveZeros = randperm(intNumZeros,round(intNumZeros*(2/3)));

Answer 2

[Jan]

With FEX: RunLength:

A      = [1.140,0.590,0.140,0,0,0,0,0,0,0,0,0,0,0,0,1,3,5];
[B, N] = RunLength(A);
N(B == 0 & N > 4) = 4;
leanA  = RunLength(B, N);

Now all runs of zeros have a maximum length of 4.