# Map between two cell arrays

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Nicolas Douillet il 11 Dic 2019
Modificato: Nicolas Douillet il 11 Dic 2019
Hi,
I want to map two cell arrays.
Following the Containers.Map documentation it is possible : "Keys, specified as a numeric array, cell array of character vectors, or string array."
But if I try :
V = num2cell(rand(5,3));
K = num2cell([1 2; 3 4; 5 6; 1 2; 3 4]);
Then :
M = containers.Map(K,V);
I get the error :
Error using containers.Map
Unsupported key specified. See documentation for valid key types.
However K and V are both 5 x 1 cell arrays. What am I missing here ?
Thanks for help.
Nicolas
Edit : I would like each row of V matching with its key row in K.
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Stephen23 il 11 Dic 2019
Modificato: Stephen23 il 11 Dic 2019
"You are right, there may be several values for a given key. "
In that case, if you use a key with multiple values do you expect MATLAB to return:
1. one value (e.g. the last one defined using that key), or
2. all of the values that have that key?
Nicolas Douillet il 11 Dic 2019
Modificato: Nicolas Douillet il 11 Dic 2019
All the values of course.
Context is : I am creating an exact grid simplify point set function. In this function I want to replace every vertices of a cell (a vertex cluster then) by the closest vertex to the cell isobarycentre (not by the barycentre istelf which is the approximate version). A key set is 3D cell index (I simplified with only two integer in the previous example). First value set would be the original vertices set, and second one would be the barycentre set (smaller than the vertices set since there may be several vertices for a same barycentre). So in the end yes, I think I would need two maps, sharing the same key set.
Edit : I forgot to mention : I would like to do this without for loop.

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### Risposta accettata

Stephen23 il 11 Dic 2019
"All the values of course."
Then you cannot use containers.Map: even if you manage to sort out everything else (those numeric inputs, rows, etc) it will only return one value (the last one) if a key has been defined multiple times:
>> K = { 'x', 'y', 'x'};
>> V = {'cat','sat','mat'};
>> C = containers.Map(K,V);
>> C('x')
ans =
mat
However you could easily use basic MATLAB indexing
>> V = rand(5,3)
V =
0.81472 0.09754 0.15761
0.90579 0.2785 0.97059
0.12699 0.54688 0.95717
0.91338 0.95751 0.48538
0.63236 0.96489 0.80028
>> K = [1,2;3,4;5,6;1,2;3,4]
K =
1 2
3 4
5 6
1 2
3 4
>> want = [3,4];
>> X = ismember(K,want,'rows');
>> V(X,:)
ans =
0.90579 0.2785 0.97059
0.63236 0.96489 0.80028
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