how find idx string deleted

a={'aa','bb','cc','aa'}

a = 1×4 cell array
    {'aa'}    {'bb'}    {'cc'}    {'aa'}

unique(a,'stable')

ans = 1×3 cell array
    {'aa'}    {'bb'}    {'cc'}

%i want to find idx string deleted..( idx=4)

Answer 1

[Fangjun Jiang]

a={'aa','bb','cc','aa'};

[b,ida,idb]=unique(a,'stable')

b = 1×3 cell array
    {'aa'}    {'bb'}    {'cc'}

ida = 3×1

1 2 3

idb = 4×1

1 2 3 1

setdiff(1:numel(a),ida)

ans = 4