deleting of rows in a matrix

Hello Every one ;

I have an matrix that occurs with time step 0.0004 .And my step end time 0.312.But I want only the datas that 0.004 and multiples of 0.004. How can I write this code

For ex

[0.02 2 8

0.04 3 2

0.08 3 3

0.01 4 6

0.012 5 2

0.014 6 3

0.016 7 2] is existing and

[0.04 2 8

0.08 3 3

0.12 5 2

0.16 7 2] is that ı want

Answer 1

[Cris LaPierre]

I'd use a logical array (Ch 12 of MATLAB Onramp) created by ismember. I had to fix some values of A.

% Original matrix
A=[0.02     2    8                                                               
0.04      3    2
0.08      3    3
0.1      4    6
0.12    5     2
0.14    6    3
0.16    7    2];

% Desired steps
B=(0.04:0.04:0.16);

% Use logical indexing to extract just the desired rows
C = A(ismember(A(:,1),B),:)

C = 4×3

0.0400 3.0000 2.0000 0.0800 3.0000 3.0000 0.1200 5.0000 2.0000 0.1600 7.0000 2.0000

% Alternate - delete the rows that are not wanted
A(~ismember(A(:,1),B),:)=[]

A = 4×3

0.0400 3.0000 2.0000 0.0800 3.0000 3.0000 0.1200 5.0000 2.0000 0.1600 7.0000 2.0000

[Omer Utku Altindag]

This is cool but not working complately.My matrix is a 3501x4 double matrix and time step is 0.001.When I put an desired time step such as B=(0:0.004:0.312) 79x1 double matrix.And when I Use logical indexing to extract just the desired rows C = A(ismember(A(:,1),B),:) and C has 59X1 double matrix.There are things that disappear about 20 datas.Can you give more information ?

[Cris LaPierre]

You are the one with all the information. Can you provide your actual data? Save it to a mat file and attach it to your post using the paperclip icon.

[Omer Utku Altindag]

I uploaded the files now :)

[Steven Lord]

I would use ismembertol instead of ismember to account for floating point arithmetic.

x = 0.1;
y = x + x + x; % 0.3 right?
isPoint3 = y == 0.3 % false, y is close but not exactly 0.3

isPoint3 = logical
   0

difference = y - 0.3 % very small

difference = 5.5511e-17

ismember(y, 0.3) % false, not exactly equal

ans = logical
   0

ismembertol(y, 0.3) % true, it's close enough

ans = logical
   1

[Omer Utku Altindag]

Now the problem is fixed.Thank you both of you !!!