Remove array values with multiple occurances from "parent" array

1 vue (au cours des 30 derniers jours)
Joe I
Joe I le 9 Juil 2020
Modifié(e) : Bruno Luong le 10 Juil 2020
How do you remove values in an array from a "master database" array? For example:
a = [1, 1, 1, 2, 2, 2, 3, 3, 3, 4, 4, 4]
b = [1, 1, 2, 4, 4, 4]
I would like to remove each occurance of each value in 'b' from 'a' to get:
c = 1, 2, 2, 3, 3, 3
setdiff(a, b) doesn't work because it removes all instances from 'a' including the repeating values (it even says no repetitions in the documentation):
c = 3
[~, col] = ismember(b, a)
a(col) = []
doesn't work because it only removes one instance of the numbers (the first index where it occured):
c = 1, 1, 2, 2, 3, 3, 3, 4, 4
Thanks for the help.

Réponse acceptée

David Hill
David Hill le 9 Juil 2020
Modifié(e) : David Hill le 9 Juil 2020
a = [1, 1, 1, 2, 2, 2, 3, 3, 3, 4, 4, 4];
b = [1, 1, 2, 4, 4, 4];
c = a;
for i=b
c(find(c==i,1))=[];
end
  1 commentaire
Joe I
Joe I le 9 Juil 2020
Modifié(e) : Joe I le 9 Juil 2020
Awesome, thanks! Works great, scales up to my datasets with tens of thousands of values in each. Seems so obvious now after seeing it. Just be sure that each variable is a row vector.

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Plus de réponses (1)

Bruno Luong
Bruno Luong le 10 Juil 2020
Modifié(e) : Bruno Luong le 10 Juil 2020
Test samples
a = [1, 1, 1, 2, 2, 2, 3, 3, 3, 4, 4, 4]
b = [1, 1, 2, 4, 4, 4]
Code
u = unique([a,b]);
n = length(u);
[~, ia] = ismember(a,u); na = accumarray(ia(:),1,[n 1]);
[~, ib] = ismember(b,u); nb = accumarray(ib(:),1,[n 1]);
c = repelem(u,max(na-nb,0))
Result
c =
1 2 2 3 3 3

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