Percentiles without Statistics Toolbox

Hi,

I have a bunch of histograms from which I need to extract some percentiles (10th, 50th and 90th).

I know about the prctile function, but it requires the Statistics Toolbox in Matlab which I do not have. The only toolbox I have is the Signal Processing Toolbox.

Is there a way of obtaining percentiles other than the prctile function?

//AM

Answer 1

[Star Strider]

Try this:

x = 3*randn(1,100)+5;                                                   % Create Data

figure
yyaxis left
h = histogram(x, 20);
hold on
barvals = h.Values;
edgs = h.BinEdges;
ctrs = edgs(1:end-1) + (diff(edgs)/2);                                  % Calculate Bar Center Locations
plot(ctrs, barvals, '+r')
hold off
ylabel('Number')

auc = 100*cumsum(barvals)/sum(barvals)+(0:numel(barvals)-1)*eps*100;    % Cumulative Area
prctls = [10, 50, 90];                                                  % Desired Percentiles
prctlctrs = interp1(auc, ctrs, prctls);                                 % Percentile X-Locations

yyaxis right
plot(prctlctrs, prctls, 'dg', 'MarkerFaceColor','g')                    % Plot Percentiles
hold on
plot(ctrs, auc, '--k')                                                  % Plot Area (Optional)
hold off
grid
ylim([0 100])
xlabel('X')
ylabel('Cumulative Percent')
text(prctlctrs, prctls, sprintfc('%2d^{th} Percentile = %5.2f\\rightarrow  ', [prctls; prctlctrs].'), 'HorizontalAlignment','right', 'VerticalAlignment','middle')
legend('Histogram', 'Centres', 'Percentiles', 'Area', 'Location','E')

.

[ava mazaheri]

Gave a perfect plot, thanks a lot!

[Star Strider]

As always, my pleasure!

[MikaelTulldahlCPAC]

if anyone needed percentiles unrelated to histograms, it's easy to calculate:

samplePoints = [0.1, 0.5, 0.9];

data = randn(10,3) % 3 sets with 10 samples each

percentiles = interp1(linspace(0, 1, size(data,1)), sort(data), samplePoints);