separate specific values from matrix

how to separate column 1 values 4541,4546,4546... and their corresponding column 2 values 0,1,2... in a separate matrix

sample matrix

 4541  0
4556  0.025
4558  0.05
4561  0.075
4559  0.1
4559  0.125
4561  0.15
4560  0.175
4561  0.2
4561  0.225
16  0.25
12  0.275
10  0.3
10  0.325
11  0.35
10  0.375
12  0.4
10  0.425
10  0.45
11  0.475
10  0.5
10  0.525
11  0.55
10  0.575
12  0.6
10  0.625
10  0.65
12  0.675
10  0.7
10  0.725
10  0.75
10  0.775
11  0.8
11  0.825
10  0.85
11  0.875
10  0.9
11  0.925
11  0.95
10  0.975
4546  1
4557  1.025
4559  1.05
4561  1.075
4559  1.1
4561  1.125
4561  1.15
4561  1.175
4562  1.2
4561  1.225
17  1.25
12  1.275
10  1.3
11  1.325
11  1.35
10  1.375
12  1.4
10  1.425
10  1.45
12  1.475
10  1.5
11  1.525
10  1.55
10  1.575
11  1.6
10  1.625
10  1.65
11  1.675
10  1.7
11  1.725
10  1.75
10  1.775
12  1.8
10  1.825
11  1.85
10  1.875
10  1.9
12  1.925
10  1.95
10  1.975
4546  2
4557  2.025
4560  2.05
4560  2.075
4559  2.1
4561  2.125
4561  2.15
4561  2.175
4561  2.2
4559  2.225

end

Answer 1

[Thorsten]

 ind = find(X(:, 1) > 4000);
 Y = X(ind, :);

[shanmukh]

i don't get the required output.

can you let me know how to find the least number, greater than 4000 in every 40 rows in column 1 and corresponding value in column 2

[Thorsten]

If X is the sample matrix you provided, Y contains only the rows of X where the value of the first column is > 4000.

Y =

1.0e+003 *

    4.5410         0
    4.5560    0.0000
    4.5580    0.0001
    4.5610    0.0001
    4.5590    0.0001
:

What do you want instead?

[shanmukh]

how to find the first least number, greater than 4000 in every 40 rows in column 1 and corresponding value in column 2

[Thorsten]

Sorry, I haven't realized that you are only interested in the first row of a greater 4000 block. Here is how you can do it

 ind = find(diff(X(:, 1)) > 4000) + 1;
 if X(1,1) > 4000, ind = [1; ind]; end
 Y = X(ind, :)