MATLAB: How to delet multiple rows with single criteria in matlab

Question

I have 900 by 4 mixed data. The first column contains letter of atom and the rest column is the XYZ coordinates of the atom. The arrangement of the atom looks like H1;H2;H3………. this three rows repeat it self until the number of rows are 900.

    x  y  Z
H1  1  2  3
*H2  2  4  7*
H3  3  0  0
H1  1  1  1
*H2  0  0  0*
H3  4  6  7
.
.
.
.
 So how can  i  remove those three rows ( H1;H2;H3) if x of H2 >=3 else keep it.the data is a cell array.The main point is i only take as a criteria the value of x corresponds to H2. From 900 rows 300 of them are H2.For instance If the first H2(second row) satisfy the criteria i want to delet H1;H2;H3 and got the next H2.If it doesn't satisfy the criteria  i will keep the three rows and go to the next H2.

Answer 1

Step 1: reshape the cell array so each row is H1 x y z H2 x y z H3 x y z:

new_c = reshape(c', 12, [])';

Step 2: find out which of the row of the reshaped cell array has x of H2 (column 6) above your threshold

rowstodelete = cell2mat(new_c(:, 6)) > 3;

Step 3: delete these rows:

new_c(rowstodelete, :) = [];

Step 4: reshape back to original n*4 columns

new_c = reshape(new_c', 4, [])'