Append indices to vector from container map

I have the above mentioned issue when I try to run this code:

I create the following container map "M" from the datastructure DS

keys = {DS.UserNum}; #UserNum
valueSet = {DS.CarNum}; #Contact_Num
M = containers.Map(keys,valueSet)

UserNum Contact_Num

1 [2 4]

2 5

3 [1 2 4]

4 [2]

5 []

Without the need for a for-loop or the initial data structure DS, I want to create a vector containing user numbers which have been in contact with UserNum 2 (in this case we will have vector containing 1,3 and 4).

Best :)

Answer 1

[Walter Roberson]

That cannot be done in MATLAB under the restrictions you put on.

containers.map does not offer any operations that affect all key/value pairs.

You can hide the for loop with cellfun, but a loop still has to be present at some level.

Side note: if you were to use digraph() objects there would be built-in support for this kind of query.

[Mehdi Jaiem]

Yes a possible solution with cellfun is still possible in my case. What function or logic could be useful if I had to use it?

[Mehdi Jaiem]

I tried the following manipulation but it did not work

b = 100001;
out = cellfun(@(x) ismember(b, cell2mat(x)), valueSet);

[Walter Roberson]

present = cellfun(@(x)ismember(b, x), values(M));
keylist = keys(M);
found_at = keylist(present);

Answer 2

[Steven Lord]

Like Walter suggested I'd use a digraph for this sort of operation. You can build a digraph from your containers.Map object. Let's start off with the containers.Map object.

cm = containers.Map('KeyType', 'double', 'ValueType', 'any');
cm(1) = [2 4];
cm(2) = 5;
cm(3) = [1 2 4];
cm(4) = 2;
cm(5) = [];

Now each key-value pair becomes some of the edges in the digraph.

D = digraph;
thekeys = keys(cm);
for whichkey = 1:length(cm)
    k = thekeys{whichkey};
    D = addedge(D, k, cm(k));
end
plot(D)

Now the answer to your question, who's been in contact with person 2, is the predecessors of 2 in the digraph.

P = predecessors(D, 2)

P = 3×1

1 3 4

You could also recreate the containers.Map object from the digraph.

cm2 = containers.Map('KeyType', 'double', 'ValueType', 'any');
for n = 1:numnodes(D)
    cm2(n) = successors(D, n);
end
% check
cm2(3)

ans = 3×1

1 2 4

cm2(5)

ans =

  0×1 empty double column vector