Assigning values from one array to another if certain specifications are met.

I have a few arrays

A=   0     1     2     3     6     8     9    10
     0     0     0     0     0     0     0     0
     0     0     0     0     0     0     0     0
     
B=  20     5    15    10
     9     8     2     1
     
C=  10    15
     9     3

Bassically the first row of A contains special points from a line that goes from 0 to 10 and the other two rows are where the values from B( to second row) and C( to third row) should go. Second rows of B and C are corresponding points from the first row of A.

For example. Since B(2,1)=A(1,7) then B(1,1) should go to A(2,7) like this:

A=   0     1     2     3     6     8     9    10
     0     0     0     0     0     0    20     0
     0     0     0     0     0     0     0     0

The final result should look like this:

A=   0     1     2     3     6     8     9    10
     0    10    15     0     0     5    20     0
     0     0     0    15     0     0    10     0

I am very much still a beginner in Matlab. I am writing a script that would calculate shear forces and bending moments of a cantilever beam so any advice and/or suggestions would be greatly appreciated.

Answer 1

[Adam Danz]

Inputs:

A=  [ 0     1     2     3     6     8     9    10
    0     0     0     0     0     0     0     0
    0     0     0     0     0     0     0     0];

B= [ 20     5    15    10
    9     8     2     1];

C=  [10    15
    9     3];

Solution:

[isMatch, col] = ismember(B(2,:), A(1,:));
A(2,col(isMatch)) = B(1,isMatch);

[isMatch, col] = ismember(C(2,:), A(1,:));
A(3,col(isMatch)) = C(1,isMatch);

Result:

>> A
A =
     0     1     2     3     6     8     9    10
     0    10    15     0     0     5    20     0
     0     0     0    15     0     0    10     0

[Tadas Grauzinis]

Thank you.

[Adam Danz]

You provided good examples! Glad I could help.

[Tadas Grauzinis]

What does isMatch do in A(2,col(isMatch))?

It seems to work with just col. I understand that if it would be just A(2,col) than it would be reffering to second row all col outputs(which are just what is needed), but what does (isMatch) add?

[Adam Danz]

Good question. Suppose matrix B was

B= [ 20     5    15    10
    9     8     200     1];

There is no match for 200 so col would return 0 for that match. A(2,col) would then return an error since indices must be positive, non-zero integers. So, col(isMatch) makes sure you're only selecting col values that correspond to matches. It's a safety net.

Answer 2

[Kevin Hellemans]

Hi,

I think this should do the trick:

A=   [0     1     2     3     6     8     9    10; ...
     0     0     0     0     0     0     0     0; ...
     0     0     0     0     0     0     0     0];  
B =  [20     5    15    10; 9     8     2     1];    
C=[10    15;     9     3];

A(2,B(2,:)) = B(1,:);
A(3,C(2,:)) = C(1,:);
disp(A)

[Tadas Grauzinis]

It reads the second rows of B and C as a position and places first row elements like this.

A=[ 0 1 2 3 6 8 9 10 0;

10 15 0 0 0 0 0 5 20;

0 0 15 0 0 0 0 0 10]