Select nearest value on a vector for a given value

Hi.

I would like to know if you can help me.

I have to get the vector index where its value is closer o nearest to a given value, for example.

i have this vector.

                   0           1          2          3         4         5         6          7             index
Value    -172.0000 | -130.8750 | -89.7500 | -48.6250 | -7.5000 | 33.6250 | 74.7500 | 115.8750 | 157.0000

and if i want to look for the -8, it want to get the index 3 because -8 is between .-48.625 and -7.5, and so on, if i looking for 157, i should get the index 7

i have this code by far, but it isnt working the way i want.

MEQ=[fil,col];

 for i=1 :fil%i will store the index in a matrix, so i have to loop over rows
     for j=1 :col%loop over matrix columns
         for w=1 :numel(recta)%this is the vector
             [c,indice]=min(abs(recta-E(i,j)));%here i get the index

                 MEQ(i,j)=indice;%change the current vector value for the index

         end
     end
 end

can some one give me an idea please

Thank you

Answer 1

[Roger Stafford]

I notice that your vector 'Value' has ascending elements. If we can assume that, the following can be used:

   s = -8;  % Or whatever value is being sought
   index = sum(Value<s)-1;

Note that this will give a -1 result if s is smaller than all the elements of 'Value' or an 8 index if it is greater than all of 'Value'. If you want to prevent these two possibilities, do this afterwards:

   index = min(max(index,0),length(Value)-2);

[Luis Marcos]

Thank you, it works perfectly

Answer 2

[Fangjun Jiang]

Can you use built-in function?

X=10:10:100;
Y=1:10;
out=interp1(X,Y,12,'nearest')
out=interp1(X,Y,18,'nearest')

[Luis Marcos]

Thank you. But i cant understand what does that do.

[Fangjun Jiang]

Your code above can be replaced with just one line.

MEQ=interp1(recta,(1:length(recta))-2,E,'nearest')