How to reduce the length of a vector?

I want to reduce the length of the vector called "u1" and make it equal to 1x100.

Follows the code that I'm using:

H = smoothdata(z_a);

figure;

plot(tempo,H, 'g');

[pks,locs]=findpeaks(H, tempo, 'MinPeakProminence', 10,'Annotate', 'extents', 'WidthReference', 'halfheight');

figure;

findpeaks(H, tempo, 'MinPeakProminence', 10,'Annotate', 'extents', 'WidthReference', 'halfheight');

text(locs+.02,pks,num2str((1:numel(pks))'));

prev = 1;

prev1 = 1;

prev2 = 1;

for i = 1:length(pks)

indice1 = pks(i);

index1 = find(H==indice1);

u1 = H(prev:index1);

prev = index1;

accelerazione = z_b(prev1:index1);

prev1 = index1;

velocita = z_c(prev2:index1);

prev2 = index1;

q1 = (length(u1)/100)-0.01;

tempo1 = (0.0:0.01:q1);

tempo3 = (0.0:length(u1)-1);

time(i) = max(tempo1);

[miny1,minyidx1] = min(u1);

minx1 = tempo1(minyidx1);

figure;

subplot(2,1,1);

plot(tempo1,u1);

xlabel('Time(s)');

ylabel('Angolo');

avstr = sprintf('Ripezione n : %.1f ',i);

title(avstr);

hold on

xline(minx1,'r');

legend('Flesso estensione tronco','Finish');

%%media

media = mean(u1);

v(i) = media;

%%media accelerazione

media_acc = mean(accelerazione);

acc_media(i) = media_acc;

%%media velocita angolare

media_veloc=mean(velocita);

veloc_media(i) = media_veloc;

%%varianza

varianza = var(u1);

t(i) = varianza;

%%deviazione standard

deviazione = sqrt(varianza);

o(i) = deviazione;

subplot(2,1,2);

X_axis_normalize = (tempo3/(numel(tempo3)))*100;

plot(X_axis_normalize,u1);

[miny,minyidx] = min(u1);

minx = X_axis_normalize(minyidx);

hold on

xline(minx,'r');

legend('Flesso estensione tronco','Finish');

xlabel('%Cycle');

ylabel('Angoli');

figure;

subplot(2,1,1);

plot(tempo1,accelerazione);

hold on

plot(tempo1,ones(length(tempo1),1)*acc_media(i));

xlabel('Time(s)');

ylabel('Accelerazione(m/s^2)');

avstr1 = sprintf('Ripezione n : %.1f ',i);

title(avstr1);

gravstr1 = sprintf('Valore medio: %.1f ',acc_media(i));

legend('Accelerazione(m/s^2)', gravstr1);

subplot(2,1,2);

plot(tempo1, velocita);

hold on

plot(tempo1,ones(length(tempo1),1)*veloc_media(i));

xlabel('Time(s)');

ylabel('Velocità angolare(rad/s)');

gravstr2 = sprintf('Valore medio(rad/s): %.1f ',veloc_media(i));

legend('Velocità angolare(rad/s)', gravstr2);

end

Answer 1

[Amrtanshu Raj]

Hi,

I am assuming that you are trying to reduce the number of points in a signal while keeping the overall characteristics unchanged. You can interpolate 100 points in between the start and end values of the vector u1 along the vector u1. You can make use of the following code:

new_points =  linspace(0,length(u1),100); 
new_u1 =  vals = interp1(u1,new_points); 

You can explore the various option available for interpolation here.

Note - Reducing the data size by a huge value can lead to loss of some critical data points

And in case you just want to trim the u1 vector from start to end you can use the following:

u1(101:end) = []; % keep starting 100 values 
u1(1:end-100) = []; % keep last 100 values