finding elements in a vector from another vector

I'd like to create a vector y with the positions of the elements of x in m.

i.e.

x=0 (first element of x) has and index of 1 in m. So y(1)=1

x=241 (second element of x) has index of 242 in x. So y(2)=242

m and x are in attached

Answer 1

[Star Strider]

Try this:

M = load('m.mat');
X = load('x.mat');
m = M.m;
x = X.x;
[~,y] = ismembertol(x, m, 1E-4)

producing:

y =
           1
         242
         937
        2001
        3306
        4695
        6001
        7065
        7759
        8001

I checked that separately for a few values using find, and it appears to produce the correct result.

.

[Paul Rogers]

can't make it work since I think m and x are in my script, I don't need to lload them.

[Star Strider]

I needed to load them. If they are already in your workspace as ‘x’ and ’m’, just run:

[~,y] = ismembertol(x, m, 1E-4)

You should get the same result that I did.

.

[Paul Rogers]

I did but I get this.

maybe it's because I have r2014b?

Undefined function 'ismembertol' for input arguments of type 'double'.

[Star Strider]

The ismembertol function was introduced in the next release, R2015a.

The only work-around I can offer is this loop:

for k = 1:numel(x)
    y(k) = find(m <= x(k), 1, 'last');
end

It produces almost the same result. They are identical, except for ‘y(3)’ that using ismembertol is 937 and using find is 936.

EDIT — (18 Jul 2020 at 20:52)

Unfortunately, ismember only works for 4 of the members of ‘x’. However that can be remedied by multiplying them by :

[~,y] = ismember(fix(x*1E+4), fix(m*1E+4))

producing essentially the same result as ismembertol, and the same results as the find loop.

[Paul Rogers]

this worrks better:

[~,y] = ismember(fix(x*1E+4), fix(m*1E+4))

thanks.

[Star Strider]

Great!

I did not initially pick up on your posting the Release information as R2014b (so my apologies for that oversight if you posted it originally, since I only checked later).

.

[Paul Rogers]

I think it's best we don't edit comment so people can read different options and figure it out based on their version

[Star Strider]

Noted.

Answer 2

[Fangjun Jiang]

[~,y]=ismember(x,m)