how to find the index of the row

Hi,

I want to get the row number in the following case. Say one has a 5 by 1 vector [1;2;3;4;5].

If I have the scalar '4.5' (which is not in that vector) then I know that 4.5 is between 4 and 5. What I want is to compare 4.5 with all the numbers in the vector. Then Matlab should be able to tell that 4.5 is between 4 and 5. My goal is to get the row number of the scalar '4'.

Consequently, if I have a scalar '3.5' then Matlab should be able to tell that 3.5 is between 3 and 4, and in this case I would like to obtain the row number of the scalar '3'

I just do not know how I could code this in Matlab.

Many thanks

Answer 1

[James Tursa]

If you are looking for the closest value:

x = your vector
s = your scalar
[~,row] = min(abs(x-s));

If you are looking for the first number <= your scalar and x is sorted increasing:

row = find((x-s) >= 0,1);

If something else, please specify.

[Imner Renmi]

Ok so what I want is to find the two closest values for a certain number (I am going to use a 5000 by 1 vector but this is just an example). In the case of 3.5 the two closest values are 3 and 4.

In my case I could get for example a number 3.772 and I would like to find the two closest values to this scalar from my vector x which is a 5000 by 1 vector. I hope you know what I mean (?)

[James Tursa]

Does the posted code ( row and row+1 ) do what you want? Or Azzi's or Andrei's Answers?

[Imner Renmi]

Yes, The first code does seem to do what I want. If something strange occurs I'll just post a new question. Thanks a lot for your help.

Answer 2

[Azzi Abdelmalek]

v=[8;6;1;2;3;7;5;4]
m=3.5
mv=[m ;v]
[ii,jj]=sort(mv)
idx=find(jj==1)
% m is between a1 and a2, 
idx1=jj(idx-1)
idx2=jj(idx+1)
a1=mv(idx1)
a2=mv(idx2)

Answer 3

[Andrei Bobrov]

p =  [1;2;3;4;5]
z = [3.5,4.5]

[~,out] = histc(z,p)