MATLAB: Count if a vector has at list one element greater than zero

conditioncountMATLAB and Simulink Student Suitevector

Hello everyone, I'm looking for a way to update a count if a vector has at least one element greater than zero.

I mean for example:

count=0;
v=rand(100,1); 
%check if v has at least one element greater than zero, if yes 
count=count+1;

Thank you

Best Answer

count = sum(v>0)

The expression v>0 creates a logical array of 1s and 0s, with a 1 for every element of v that is greater than zero. Summing all values in the logical array therefore gives the total number of elements greater than zero.

(By the way, the rand function only generates positive numbers between 0 and 1, so to create random numbers between -1 and 1, you would use 1-2*rand.)

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MATLAB: Counting consecutive occurences of 1s and -1s

The first step below counts all consecutive numbers. The second step eliminates the 0-counts.

A = [0 0 1 1 1 1 0 0 0 -1 -1 -1 0 1 1 0 ]; 
changeIdx = [1,diff(A)]~=0; 
counts = histcounts(cumsum(changeIdx),1:sum(changeIdx)+1); 
consecutiveCounts = [A(changeIdx)',counts']
% Result:
consecutiveCounts =
     0     2            %First there are 2 zeros
     1     4            %then 4 ones
     0     3            %then 3 zeros
    -1     3            %then 3 negative ones
     0     1            % etc...
     1     2
     0     1

To get the vector you described, eliminate the 0-counts and multiply by the sign of the value in A so counts of negative numbers are negative.

  consecutiveCounts(consecutiveCounts(:,1)~=0,2)' .* sign(consecutiveCounts(consecutiveCounts(:,1)~=0,1))'
ans =
     4    -3     2

MATLAB: Efficient way to count the number of times a value changes to a particular value in an array

sum(x(2:end)==1 & x(1:end-1)~=1)

Best Answer

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MATLAB: Counting consecutive occurences of 1s and -1s

MATLAB: Efficient way to count the number of times a value changes to a particular value in an array

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