MATLAB: How to declare all the rows and all column in matlab in a matrix or array?

neural network

suppose i need to remove all the zeros from a dataset and within a if else condition if the i no rows found zeros with all its column then the entire row will be deleted .. i need to know how to declare the entire row with column in matlab

is this the way to write c(:)=[]

Best Answer

"if [...] rows found zeros with all its column then the entire row will be deleted"

If the array is x, then

idx=~any(x,2);  % logical vector T for rows all zero
x(idx,:)=[];    % remove those rows

NB: other scattered zeros will still be in the array and there's no way to remove them and keep a 2D array unless there's a fixed number in each row/column so the resulting length of each reduced row and column is a constant. This is an unlikely condition in general altho could be possible for specific cases.

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MATLAB: How to make a variable that is equal to the position of a row in a table by using the name of that row

fieldnames is specically documented for struct or Java or COM objects at least thru R2019b; I wasn't aware it would return the column names from a table object. There's no parallel for the row identifiers like rownames however.

fieldnames seems to return the table variable names first and is followed by the elements {'Properties','Row','Variables'} irrespective of the values of those additional property values. Hence, it's not particularly useful for that purpose.

But, it's simple enough, just use the table .Row property...

find(ismember(T.Row, 'Name of Row'))

There is also the T.Properties.RowNames property that returns the row names cellstr array.

I tend to write using newer string class functions like contains or beginsWith instead of ismember although the row names internally are and are returned as a cellstr array.

MATLAB: Check for value in multiple columns and delete rows with that value

If ‘M’ is your matrix, this will work:

idx = any(bsxfun(@eq, M(:,1), (M(M(:,3)==-1,1))'),2);
Mout = M(~idx,:);

The ‘M(M(:,3)==-1,1)’ checks column 3 for -1 values, and returns the corresponding values in column 1. The bsxfun call searches for elements of column 1 that are equal to those values, and returns a matrix of column vectors of logical indices for each equality. The any call will be 1 if any of the column vectors are 1 in all rows, creating a single column logical vector from the matrix of logical vectors. Then the ‘Mout’ assignment returns all the rows that are not 1, producing the desired output.

Also, you can avoid retyping the ‘idx’ assignment with your actual array name by creating an anonymous function from it, so that if you call your array ‘A’:

idxfcn = @(M) ~any(bsxfun(@eq, M(:,1), (M(M(:,3)==-1,1))'),2);
idx = idxfcn(A);
Result = A(~idx,:);

producing the desired result.

Best Answer

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MATLAB: How to make a variable that is equal to the position of a row in a table by using the name of that row

MATLAB: Check for value in multiple columns and delete rows with that value

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