Inserting Elements in middle of 1-D, 2-D, N-D Array

Dear All,

I have got an array X = [1 2 3 4 5].

Want to refine the points by averaging neighbours and insert in the middle.

X1 = [1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0].. So, 5 points have become 9 points.

Is there an easier way to do it for a general array?

I would like to make it work in N-dimension also ... for refining the points.

Any help is much appreciated.

Thank You in advance,

K Vijay Anand.

Answer 1

[Ameer Hamza]

interp1() is suitable for such cases.

X = [1 2 3 4 5];
n_new = 9;
X_new = interp1(linspace(0,1,numel(X)), X, linspace(0,1,n_new))

For a high-dimensional case, you need to specify whether you want to apply it on a single dimension or all the dimensions?

[Vijay Anand]

Thank You Mr.Ameer Hamza.

Amazing Logic !!!

Can you make it work for higher Dimensions also.

X = [

1.0 2.0 3.0

4.0 5.0 6.0

7.0 8.0 9.0

]

becomes,

X1 = [

1.0 1.5 2.0 2.5 3.0

2.5 3.0 3.5 4.0 4.5

4.0 4.5 5.0 5.5 6.0

5.5 6.0 6.5 7.0 7.5

7.0 7.5 8.0 8.5 9.0

]

Thanks in advance.

-Vijay

[Ameer Hamza]

Try interp2():

X = [
  1.0  2.0  3.0 
  4.0  5.0  6.0 
  7.0  8.0  9.0
];
new_size = [5 5];
[xg, yg] = meshgrid(linspace(0,1,size(X,2)), linspace(0,1,size(X,1)));
[xg_, yg_] = meshgrid(linspace(0,1,new_size(2)), linspace(0,1,new_size(2)));

X_new = interp2(xg, yg, X, xg_, yg_);

or interpn() for a more general solution.

Answer 2

[Stephan]

This may help

https://de.mathworks.com/help/matlab/ref/griddedinterpolant.html

X = [
  1.0  2.0  3.0 
  4.0  5.0  6.0 
  7.0  8.0  9.0]

F = griddedInterpolant(X)
[xq,yq] = ndgrid(1:0.5:3);
Vq = F(xq,yq)

results in:

X =

     1     2     3
     4     5     6
     7     8     9


F = 

  griddedInterpolant with properties:

            GridVectors: {[1 2 3]  [1 2 3]}
                 Values: [3×3 double]
                 Method: 'linear'
    ExtrapolationMethod: 'linear'


Vq =

    1.0000    1.5000    2.0000    2.5000    3.0000
    2.5000    3.0000    3.5000    4.0000    4.5000
    4.0000    4.5000    5.0000    5.5000    6.0000
    5.5000    6.0000    6.5000    7.0000    7.5000
    7.0000    7.5000    8.0000    8.5000    9.0000

[Vijay Anand]

Thank a lot Mr.Stephan,

Works perfectly fine and solves my requirement !!!

Cheers,

Vijay