How to select specific matrix rows trough specifik given numbers

Hey guys. Im working on a project where i have i to pick out specific rows in one N x 6 matrix matching a specifik given value.

Then using the placement of those specific rows in order to calculate data within those specific rows in a different N x 4 matrix.

The rows within the N x 6 matrix is combined like: [ year , month , day , hour , minute , second ]

So for an example i need to find all rows with the hour 15, i find two rows in that specific dataset one in row 4 and one in 10. I then need to calculate the exact same rows within the N x 4 matrix.

Any ideas to how this is done?

i've tried out with A(: , 4==15) but that doesn't tell the sepcific rownumber.

[vimal kumar chawda]

First mention the number of loop with some i and after that mention at which number of loop the requirement fulfill. And if the loop number is 5 then it should stored the value at position 5th. all other matrix will be 0 and the you will get row number.

Or you can mention with another variable with k so if i all requirement fulfill then stores the x value which is row (x,y). you have to define the iteration perfectly.

[Image Analyst]

vimal - please put down below in the Answer section with the rest of the answers. Thanks in advance.

Answer 1

[Image Analyst]

Try this:

% Determine which rows to extract:
rowsToSelect = A(:, 4) == 15;
% Make a new matrix with only those rows extracted:
extractedRows = A(rowsToSelect, :);

[Joakim Mørk]

Could this action be automated, say i have 'n' rows with 24 different values i want to apply this command to but without having to write the same command 24 times?

[Joakim Mørk]

And could you do the same command but without knowing the valubel to set equal?

% Extracting rows of value 'n':
rowsToSelect = A(:, 4) == n;
% Make a new matrix with only those rows extracted:
extractedRows = A(rowsToSelect, :);

[Image Analyst]

You should put all your n in some vector, like

n = [15,123,4234,22,3423, etc for all your 24 values]

Then you'd do something like this:

for k = 1 : length(n)
    % Get the k'th value of n
    this_n = n(k);
    % Determine which rows to extract:
    rowsToSelect = A(:, 4) == this_n;
    % Make a new matrix with only those rows extracted:
    extractedRows = A(rowsToSelect, :);
    % Now process extractedRows in whatever way you want to...
end

If your n are sequential, you can do

n = 1 : 24;

then the for loop I had above, or else you can do

for k = 1 : n
    % Determine which rows to extract:
    rowsToSelect = A(:, 4) == n;
    % Make a new matrix with only those rows extracted:
    extractedRows = A(rowsToSelect, :);
    % Now process extractedRows in whatever way you want to...
end

Answer 2

[Tommy]

If A is your N x 6 matrix and B is your N x 4 matrix,

B(A(:,4)==15,:)