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MATLAB Array Operations

  1. Jul 7, 2008 #1
    Hi,

    How can I find the following from an array with entries of 0, 1, and >1:

    Find the sum of all the entries in the matrix that are not equal to 0.
    Find the sum of all the entries in the matrix.
    Find the sum of all the zero and 1 entries in the matrix.
    How to remove the entries in the matrix that are not equal to 0, one by one.

    Thanks!
     
  2. jcsd
  3. Jul 7, 2008 #2
    I guess I can simplify my question:

    I have a matrix A that contains values of 0, 1, and values that are greater than one. I need to remove the entries in the matrix that are greater than 1 until the number of values that are 0 and 1 outnumber the number of values that are greater than 1. Then I need to display the new matrix B that contains the result of the aforementioned operation.

    Hope that helps and thanks in advance!
     
  4. Jul 7, 2008 #3
    Alright, so I have this so far:

    function[newInteractions]=prune(interactions)

    while( sum(interactions(interactions~=0)) > sum(interactions(interactions<=1)) )

    i=max(interactions);

    interactions(i)=[];

    end

    newInteractions=interactions;

    I have a feeling that this can be improved in terms of speed -- the max function seems to be very slow. Can this be improved?
     
  5. Apr 27, 2009 #4
    Hi

    If you array is something like:

    A=[1 0 0 0 1 0 1 0 25 5 8 69 0 0 1 0 1 0 1 1 1 1 0 4 7 0 1]

    A quick way to remove all the bumf greater than 1 in your array is:

    A(A>1)=[];

    ______

    For your summing problems try:

    x=find(A>1) %This will return all the points greater than 1 in your data.
    y=length(x) %This will give you a number corresponding to the number of successful finds.
     
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