Using ismembertol for multiple coincidences

Question

Jose Luis Villaescusa Nadal 2022-11-2

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1841953-using-ismembertol-for-multiple-coincidences

编辑： Bruno Luong 2022-11-2

采纳的回答： Bruno Luong

在 MATLAB Online 中打开

I have two vectors, and I'm trying to find ALL coincidences of one on the other within a certain tolerance.

For example:

A = [5 3 4 2]; B = [2 4 4 4 6 8];

I want to obtain a cell array containing on each cell the numbers of all the coincidences with a tolerance of 1 (or more) units. (A = B +- 1)

I have a solution with zero units (A = B), which would look something like this:

tol = 0;
[tf, ia] = ismembertol(B,A,tol,'DataScale',1); % For tol = 0, this is equivalent to using ismember
idx = 1:numel(B);
ib = accumarray(nonzeros(ia), idx(tf), [], @(x){x}) % This gives the cell array

The output is:

ib = 
[]
[]
[2 3 4]
[1]

Which is as desired.

If I change the tolerance to 1, the code doesn't work as intended. It outputs instead:

tol = 1
[tf, ia] = ismembertol(B,A,tol,'DataScale',1); % For tolerance = 1, this is equivalent to using ismember
idx = 1:numel(B);
ib = accumarray(nonzeros(ia), idx(tf), [], @(x){x}) % This gives the cell array
ib = 
[5]
[2 3 4]
[]
[1]

When I would expect to obtain:

ib = 
[2 3 4 5]
[1 2 3 4]
[2 3 4]
[1]

What am I doing wrong? Is there an alternative solution?

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Answer 1

Bruno Luong 2022-11-2

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1841953-using-ismembertol-for-multiple-coincidences#answer_1089813

在 MATLAB Online 中打开

Using ismembertol is inappropriate

A = [5 3 4 2]; B = [2 4 4 4 6 8];
tol = 1;
[ib,ia]=find(B'<=A+tol & B'>=A-tol);
c = accumarray(ia,ib,[numel(A) 1],@(x){x'})
c = 4×1 cell array
    {[2 3 4 5]}
    {[1 2 3 4]}
    {[  2 3 4]}
    {[      1]}
c{:}
ans = 1×4
     2     3     4     5
ans = 1×4
     1     2     3     4
ans = 1×3
     2     3     4
ans = 1

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Jose Luis Villaescusa Nadal 2022-11-2

编辑：Jose Luis Villaescusa Nadal 2022-11-2

When A and B are long vectors, matlab quickly runs out of memory, since the find creates an array of size [numel(A), numel(B)]. Ismembertol, seems to be able to deal with this.

Do you think there is a way to overcome this with your solution?