I need to delete some rows in an array based on if their column values fall inside a range

I have a Nx3 matrix A. I have my conditions: xlo = 0; xhi = 100; ylo = 0; yhi = 100; zlo = 0; zhi = 100; I want to be able to go through the matrix and start at row 1, and check that the value in A(1:1) falls between xlo and xhi if it does not I want it to delete that row and move to the next row. In case that the value in A(1:1) falls between xlo and xhi I want it to move to A(1:2) and I want the value in this cell to fall between ylo and yhi, if it doesnt I want it to delete the row and move to the next one. In case the value in A(1:2) falls within the ylo and yhi range then I want it to move to check A(1:3). A(1:3) should be in the range between zlo and zhi. If it is not in between the range then delete the row and move to the next row. If all conditions are satisfactory I want it to output that row into a new matrix that is going to be a Mx3. M being the number of all the rows that passed the conditions

Answer 1

[Stephan]

Hi,

to get Matrix B (B contains every row of A that meet all conditions) use:

B = A(A(:,1)>xlo & A(:,1)<xhi & A(:,2)>ylo & A(:,2)<yhi & A(:,3)>zlo & A(:,3)<zhi,:)

see this example with random numbers:

xlo = 0;
xhi = 100;
ylo = 0;
yhi = 100;
zlo = 0;
zhi = 100;
A = randi(200,25,3);
B = A(A(:,1)>xlo & A(:,1)<xhi & A(:,2)>ylo & A(:,2)<yhi & A(:,3)>zlo & A(:,3)<zhi,:);

results in:

A =

     105   140    43
      25    41    77
      36   134     6
     142    89    95
     167    87    67
       7    36   196
     152    39   112
     192   124   170
      69    54    82
     128   112    93
      69   189   166
      44   143   199
     158   136   105
     145   192   186
      56   156   148
     117   122   114
      85   190   194
      19    12   165
       5    54   192
      99   198   130
      56   155    76
      68    96    96
      58   137   183
      35    84     3
      80    77    32

B =

      25    41    77
      69    54    82
      68    96    96
      35    84     3
      80    77    32

Deleting rows in A which not meet the conditions gives the same result by using or instead of and:

A(A(:,1)<=xlo | A(:,1)>=xhi | A(:,2)<=ylo | A(:,2)>=yhi | A(:,3)<=zlo | A(:,3)>=zhi,:) = []

Result keeps the same - so removing lines in A is not needed to achieve what you want:

A =

      25    41    77
      69    54    82
      68    96    96
      35    84     3
      80    77    32

Best regards

Stephan

Answer 2

[Jose Martinez]

%TEST%
A = CROP;
B = A(A(:,1)>xlo & A(:,1)<xhi & A(:,2)>ylo & A(:,2)<yhi & A(:,3)>zlo & A(:,3)<zhi,:);
%TEST END%

That is how I used your code and it is outputting a matrix B with no values.

This is what I was thinking off earlier but its giving me an error:

nr = 0;
nf = 0;

for nr = 0:f-1
    nr = nr + 1;
    if (CROP(nr:1) >= xlo) && (CROP(nr:1) <= xhi)
         if (CROP(nr:2) >= ylo) && (CROP(nr:2) <= yhi)
             if (CROP(nr:3) >= zlo) && (CROP(nr:3) <= zhi)
                 nf = nf +1;
                 CFinal(nf,:) = CROP(nr,:); 
             else CROP(nr,:) = [];
             end

           else CROP(nr,:) = [];
           end

      else CROP(nr,:) = [];
      end
  end

but by some reason I am getting this error in the command window:

Operands to the || and && operators must be convertible to logical scalar values.

Error in MartensiteSim (line 117)
         if (CROP(nr:2) >= ylo) && (CROP(nr:2) <= yhi)

[Stephan]

As you can see in my example the code works properly. If the output B is empty , either there are no values in A meeting all the conditions you have or possibly the conditions are choosen bad.

However the way to tacle this kind of problem is shown in this answer.

To correct the error message you can replace && by & and | | by |.

[Jose Martinez]

Got it! Thank you so much Stephan!!!

[Stephan]

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