How do i get index of a closest value from an array?

Hello ,

My array is

a=[0 200 900 1000 1200 1798 1799 1801 2000 2700 3601]

I want to find all the index of numbers which are multiples of 900. In case the multiples are not present in the array, find the index of the closest number matching the multiples.

I want to find for multiples of 900

I tried this

Index= mod(a,900) == 0 
index_chunk=find(Index == 1)

but it does not give me index of the closest number of multiples of 900.

Answer 1

[Jan Orwat]

Try something like this:

divisor = 900;
how_close_is = abs(mod(a+divisor/2,divisor)-divisor/2);
index_chunk=find(how_close == min(how_close));

or add a parameter:

closer_than = 10; % adjust to your needs
index = abs(mod(a+divisor/2,divisor)-divisor/2) <= closer_than;
index_chunk = find(index);

[yashvin]

@ Jan, if i change the closer_than=0, it picks

1     3     7     8    10    11

7 and 8 corresponds to 1799 and 1801. In fact, i want the index of any of the numbers- not both..Which approach would you suggest?

Answer 2

[Thorsten]

 N = round(max(a)/900); 
 for i = 1:N, [~, ind(i)] = min(abs(a - 900*i)); end

[yashvin]

@Thorsten

I want to include the index of the first number too ! That is index of 0 which i consider to be a multiple of 0. any change you recommend?

[yashvin]

I have many streams of a. For each stream, how can i store its corresponding ind. If I try to make ind a cell, it says error.

[Thorsten]

To include 0, use

for i = 0:N, [~, ind(i+1)] = min(abs(a - 900*i)); end

To store the indices in a cell C, when all the a's a stored in cell A:

for j = numel(A) % loop through all a's
  a = A{j};
  for i = 0:N, [~, ind(i+1)] = min(abs(a - 900*i)); end
  C{j} = ind;
end