This is not really the province of find. Yes, you can break an egg with a hammer, but it is not really the right tool for the purpose. (Ok, yes, the scrambled eggs made that way will be high in fiber. But they tend to be a little too crunchy for my tastes.) Instead, you need to learn about the set membership tools in MATLAB.
First, I'll make the problem slightly more interesting, since using the numbers 1:5 may confuse things.
y=[2:2:20]
y =
2 4 6 8 10 12 14 16 18 20
There are clearly some elements in y that are not in x, and vice versa.
help ismember
ISMEMBER True for set member.
LIA = ISMEMBER(A,B) for arrays A and B returns an array of the same
size as A containing true where the elements of A are in B and false
otherwise.
LIA = ISMEMBER(A,B,'rows') for matrices A and B with the same number
of columns, returns a vector containing true where the rows of A are
also rows of B and false otherwise.
[LIA,LOCB] = ISMEMBER(A,B) also returns an array LOCB containing the
lowest absolute index in B for each element in A which is a member of
B and 0 if there is no such index.
[LIA,LOCB] = ISMEMBER(A,B,'rows') also returns a vector LOCB containing
the lowest absolute index in B for each row in A which is a member
of B and 0 if there is no such index.
The behavior of ISMEMBER has changed. This includes:
- occurrence of indices in LOCB switched from highest to lowest
- tighter restrictions on combinations of classes
If this change in behavior has adversely affected your code, you may
preserve the previous behavior with:
[LIA,LOCB] = ISMEMBER(A,B,'legacy')
[LIA,LOCB] = ISMEMBER(A,B,'rows','legacy')
Examples:
a = [9 9 8 8 7 7 7 6 6 6 5 5 4 4 2 1 1 1]
b = [1 1 1 3 3 3 3 3 4 4 4 4 4 9 9 9]
[lia1,locb1] = ismember(a,b)
% returns
lia1 = [1 1 0 0 0 0 0 0 0 0 0 0 1 1 0 1 1 1]
locb1 = [14 14 0 0 0 0 0 0 0 0 0 0 9 9 0 1 1 1]
[lia,locb] = ismember([1 NaN 2 3],[3 4 NaN 1])
% NaNs compare as not equal, so this returns
lia = [1 0 0 1], locb = [4 0 0 1]
Class support for inputs A and B, where A and B must be of the same
class unless stated otherwise:
- logical, char, all numeric classes (may combine with double arrays)
- cell arrays of strings (may combine with char arrays)
-- 'rows' option is not supported for cell arrays
- objects with methods SORT (SORTROWS for the 'rows' option), EQ and NE
-- including heterogeneous arrays derived from the same root class
See also ISMEMBERTOL, INTERSECT, UNION, UNIQUE, UNIQUETOL, SETDIFF,
SETXOR, SORT, SORTROWS.
Documentation for ismember
doc ismember
Other uses of ismember
categorical/ismember datetime/ismember sym/ismember
cell/ismember duration/ismember tabular/ismember
codistributed/ismember gpuArray/ismember tall/ismember
dataset/ismember mtree/ismember
[yinx,xloc] = ismember(y,x)
yinx =
0 1 0 0 1 0 0 1 0 0
So which elements of y were found in x?
That makes sense. Next, where were they found?
So at locations [2,4,6] in the x vector.
You will also find the setdiff tool to be useful at times, as well as intersect and union. Spend some time familiarizing yourself with many of these fundamental tools in MATLAB. It will be well worth the time invested.
