finding certain points in data

hello,

if I have a row of data say:

x = 1, 1.4, 2, 2.2, 3, 3.7, 4.....

where the corresponding

y = 2, 3, 1, 6 ,5, 1, 5......

how do I pick the Y values that correspond to x = 1, 2, 3, 4 only

I have a few thousand points to search through and would appreciate some guidance.

thanks

Answer 1

[Walter Roberson]

If you have a list of desired x points and they are not integral then

ysubset = interp1(x, y, xsubset, 'nearest');

If you have R2015a or newer you could use

[tf, idx] = ismembertol(xsubset, x);
xfound = xsubset(tf);
ysubset = ysubset(idx(tf));

The interp1 and ismembertol techniques can also be used if your target x are integers. However, if your criteria is that you want to extract all of the values that correspond to integer x and leave out the others then,

tf = x == floor(x);
xsubset = x(tf);
ysubset = y(tf);

[harley]

thanks