MATLAB: How to change values meeting certain criteria to NaN… in certain columns only

indexingMATLABmatrixnan

I have a large matrix with 96 columns and thousands of rows. I would like to find all values values larger than 100 in even-numbered columns (2, 4, 6…) and replace them with NaN.

I know of:

A(A(:,2)>100,2) = NaN;

How can I make it work with multiple columns (:,2:2:end)?

Best Answer

B=A(:,2:2:end);
idx=B>100;
B(idx)=NaN;
A(:,2:2:end)=B

Related Solutions

MATLAB: Replace a number in a matrix depending on neighbor numbers

It is unclear if elements connected diagonally count as neighbours. If not, then you could try something like this.

%%Work with At to keep A intact
At=A;
%%Replace NaN with some number
At(isnan(At))=9;
%%B is for saving index of new NaNs
B=zeros(size(At));
%%Find sequences of [2 NaN] and [NaN 2] row-wise
for i=1:size(At,1)
B(i,strfind(At(i,:),[9 2])+1)=NaN;
B(i,strfind(At(i,:),[2 9]))=NaN;
end
%%Transpose A and repeat (same as column-wise)
At=At';
for i=1:size(At,2)
B(strfind(At(i,:),[9 2])+1,i)=NaN;
B(strfind(At(i,:),[2 9]),i)=NaN;
end
A(isnan(B))=NaN

ans =

   NaN   NaN   NaN   NaN   NaN   NaN   NaN
   NaN   NaN   NaN   NaN   NaN   NaN   NaN
   NaN   NaN     1     1     1   NaN   NaN
   NaN   NaN     1     2     1   NaN   NaN
   NaN   NaN     1     1     1   NaN   NaN
   NaN   NaN   NaN   NaN   NaN   NaN   NaN
   NaN   NaN   NaN   NaN   NaN   NaN   NaN

MATLAB: Extract a portion of vector

I solve the problem with the help of my friend, I needed two while cicle.

to solution was:

C=impuct vector and e1=C(:,2), the code is:

i=1;
while i<length(e1)
      j=0;
      i
      while isnan(e1(i+j))==0 && (i+j)<length(e1)
          j=j+1;
      end
      if j<7
          e1(i:(i+j-1))=NaN;
      end
      i=i+j+1;
  end

Best Answer

Related Solutions

MATLAB: Replace a number in a matrix depending on neighbor numbers

MATLAB: Extract a portion of vector

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