conditional data selection and saving back to file

@Star Strider @Image Analyst

I have data matrix x= row [1 :2:100] and y =row[1:2:100] same number of elements in x and y.

i want to choose data with following conditions,

for x<20 select data at interval of 5 which is [1; 6; 11; 17]

for 20<x<50 select data at interval of 10 which is [20; 30; 40; 50]

for 50<x<100 data selection at interval of 8 ......

same for y and then I have to plot x vs y

how can I easily do it for larger set of data for x and y and save it later in .txt or excel file.

Thank you.

Answer 1

[Mathieu NOE]

hello

this is my suggestion

NB the input data I have changed the delta to 1 so that it works for the tasks you asked

 clc
clearvars

x= (1:100)';
y = sin(0.25*x)+0.1*x;
 
%  i want to choose data with following conditions,
% for x<20          select data at interval of 5          which is   [1; 6; 11; 17]
% for 20<x<50    select data at interval of 10        which is [20; 30; 40; 50]
% for 50<x<100   data selection at interval of 8   ......
% same for y and then I have to plot x vs y
% how can I easily do it for larger set of data for x and y and save it later in .txt or excel file.

% below vector have length equal to number of cases stated above 
% you easily expand the number of conditions without doing manual tweaks
lim_low = [1 20 50]; % define here the lower limits of range
lim_up = [20 50 100]; % define here the uper limits of range
steps = [5 10 8]; % define here the steps

%%% main loop %%
ind = [];
for ci = 1:numel(steps)
    ind = [ind (lim_low(ci):steps(ci):lim_up(ci))]; %#ok<*AGROW>
end

ind = unique(ind); % remove duplicates if any
xx = x(ind);
yy = y(ind);

 plot(x,y,'b',xx,yy,'dr')
 A = [xx(:) yy(:)];
 writematrix(A,'out_file.txt');

[Sudhir Rai]

Thank you. It worked for my condition.

But is there a way to select data at certain interval without giving any limit (upper ..lower)

I am asking this because i want to use it for analyzing huge random data (millions).

[Mathieu NOE]

I am not sure to understand - how would you define then the intervals and steps ?

maybe I didn't understand in the first place the purpose of that code