Assign a set of values in a matrix depending on the index of it

I have two matrices from which I compute the distances between Points in P1 and P2. In P1, I have only X and Y coordinates.

P1=[12 45
    34 7 ]

and in P2 , I have the index of the point (in the first column), X and Y coordinates. The index in the first column is not sorted and it is not complete. Like in the example, I don't have indices 1,4 and 5.

P2= [2 42 25
     6 37 57 
     3 55 16]

So after computing the distances bw the points of P1 and P2, I have the result in another matrix D. Now, I have another matrix Dall, where I have rows for all points (from P2 and those not also into it). I want to put the distances I got from D inside of Dall for the corresponding rows.

What I am doing with a for loop is

for i=1:size(P1,1)
    for j=1:size(P2,1)
         x=P2(i,1);
   Dall(x,j)  = D(i,j);  
    end   
end

Any more optimal way to do it?

[etudiant_is]

If I do

Dall(P2(:,1),:)=4;

It works on the lines I want. But like this, it gives me an error.

Dall(P2(:,1),:)= D(:)

Answer 1

[etudiant_is]

What worked for me is

Dall(P2(:,1),:)= D

Answer 2

[Image Analyst]

You didn't really say what you're doing to get D. So what I did, using pdist2() in the Statistics and Machine Learning Toolbox, is

P1 = [12 45
      34 7 ]
P2 = [2 42 25
      6 37 57
      3 55 16]
distances = pdist2(P1, P2(:, 2:end))

I assume you did the same. So I got

distances =
      36.0555127546399    27.7308492477241     51.8652099195598
      19.6977156035922    50.0899191454728     22.8473193175917

The 2 rows correspond to the 2 points from P1, and the 3 columns are the distances to the corresponding 3 points in P2. But what I don't know is what you want Dall to look like.

[etudiant_is]

In my case, I am taking the transposed of the matrix distances you got(I have the lines for the indices of the points from P2.

   D=  36.0555   19.6977
     27.7308   50.0899
     51.8652   22.8473

Dall will be like this at the end

Dall =
   0          0 
   36.0555   19.6977
   51.8652   22.8473
    0         0
    0         0
   27.7308   50.0899

I am putting the other lines to 0 but in reality, there are some other values in them from previous parts and I want to keep what is inside them unchanged.

[Image Analyst]

Sorry, but we can't figure out the "rule" for how you distribute the numbers from distances into Dall.

[etudiant_is]

it is based on the value I have in the first column of P2. In this example I have 2, 6 and 3. So the first distance will be in line 2, the second in line 6 and the third in line 3 of Dall. I already found how to do it with

 Dall(P2(:,1),:)= D

Thanks