Quarter values of a vector for plotting

Hello,

I have a matrix which correspondes to the X and Y coordinates, the matrix is of size (2,m) where m is unknown. On my plot i want to label the plot at 25%, 50% and 75% of the plot (as well as the inintial and final values but i managed with those two). Is there an easy clean way to implement this or do i need to manually find the quarter points of the vector. this is what i have at the moment:

first_q = round(size(f,2)*0.25);
        second_q = round(size(f,2)*0.5);
        third_q = round(size(f,2)*0.75);
        text( f(1,1), f(2,1), sprintf('initial - %.2f', f(2,1)) )
        text( f(1,first_q), f(2,first_q), sprintf( '25%% - %.2f', f(2,first_q)), 'HorizontalAlignment', 'center')
        text( f(1,second_q), f(2,second_q), sprintf( '50%% - %.2f', f(2,second_q)), 'HorizontalAlignment', 'center')
        text( f(1,third_q), f(2,third_q), sprintf( '75%% - %.2f', f(2,third_q)), 'HorizontalAlignment', 'center')
        text( f(1,end), f(2,end), sprintf( 'final - %.2f', f(end)), 'HorizontalAlignment', 'right')

[Anmol Dhiman]

HI Benjamin,

Which specific type of plot you want to use for visualization? You can use boxplot.

Answer 1

[Aniket]

Hi @Benjamin Duvieusart,

Yes, you do need to manually find the indices corresponding to 25%, 50%, and 75% of the vector length. There is no built-in shorthand in MATLAB for “label at 25% of a vector's length” — so your use of round(size(f,2)*0.25) is actually standard and perfectly fine.

However, the code can be cleaned up slightly following below steps:

• Avoid repeating size(f,2) by assigning it once.
• Use a loop to reduce code repetition.
• Fix small typo: f(end) in your final text call should be f(2,end) for the y-value.

% Assume f is 2 x m matrix with [x; y]
m = size(f, 2);  % Number of points

% Define fractions and labels
fractions = [0, 0.25, 0.5, 0.75, 1];
labels = {'initial', '25%%', '50%%', '75%%', 'final'};
alignments = {'left', 'center', 'center', 'center', 'right'};

% Loop through and label each point
for i = 1:length(fractions)
    idx = round(1 + (m - 1) * fractions(i));
    text( f(1,idx), f(2,idx), ...
          sprintf('%s - %.2f', labels{i}, f(2,idx)), ...
          'HorizontalAlignment', alignments{i} );
end

This looks more concise and professional.

Hope this helps!