In a large matrix, find and provide location of rows containing zeros

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Louise Wilson 2019-8-22

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评论： David Hill 2019-8-23

I have a series of large matrix, 7184x72001, in which the first column is a datenum vector, and all the rows represent values for each datenum.

If a row didn't meet certain criteria, I asked my forloop to fill it with zeros. Unfortunately I didn't consider how large my matrix was and how hard it would then be to find the rows that contain zeros, if they exist. I know that in my first example, there is one row that is all zeros, excluding the datenum vector in the first column.

Is it possible to make a variable which contains the datenum value for the rows which contain zeros?

The following code, I have used to confirm that the row of zeros exist, but it doesn't tell me WHERE it is. Ideally I would get a list of datenums for the rows which are filled with zeros.

for row = 1 : size(Agoat, 1)
  zeroLocations{row} = find(Agoat(row, :) == 0)
end

Thank you everyone!

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Ted Shultz 2019-8-22

Are you only trying to find rows where every value in the row is 0?

Louise Wilson 2019-8-22

Hi Ted, thanks for response! The first column in every row has a datenumber, so I am trying to find where row 2:n(rows) will be 0. And then, get the value in the first column for that row. Does it make sense?

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Answer 1

David Hill 2019-8-22

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在 MATLAB Online 中打开

How about,

x=sum(Agoat(:,2:end),2);
Agoat(find(x==0),1);%answer matrix will contain all time stamps with zero rows.

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Louise Wilson 2019-8-23

I get that the first line creates a vector containing the sum of each row.

What exactly is the second line doing-looking for values in that which are zero? Where does it create the new vector with the datenum values?

David Hill 2019-8-23

If finds the indexes of the zero rows from the column vector x and indexes into the Agoat matrix at those indexes along the first time-stamp column to produce the datenum values of the zero rows as a column vector.

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