How to find elements of an Array using indexes.

I need to find the elements in a 388x2 array by using indexes given by [I]. The indexes can be any number within the 0-388 range and there are 31 total.

[James Tursa]

Indexes can't be 0 in MATLAB. Can you give a small example? Normally you would just do something like this:

result = my_array(I,:);

[Brandon Bush]

 SAT_RNFL = nan(31,1); %Creates a 31 x 1 array
 for i = 1:31
    [Y, I] = min((latS - latG(i)).^2  +  (lonS - lonG(i)).^2); %Finds matching Lat and Lon values
    disp(I) %Prints indices of the matched coordinates
    SAT_RNFL(i) = RNFLS(I,1); %Sticks the satellite rainfall value in the new array
 end

This is the code I use to match Lat and Lon coordinates of rain gauge and satellite precip values. The Satellite coordinates are in the 388x2 array and [I] is the indices of those values that got matched with the coordinates in the rain gauge array, which is 31x2. I need to print out the actual coordinates that got matched instead of the indices.

[Brandon Bush]

The SAT_RNFL and RNFLS arrays are just rainfall totals and have nothing to do with the coordinates

[Brandon Bush]

Also when the loop finishes, the only thing that gets mapped to I is the last value, however, when I use disp(I) it prints out all the indices

Answer 1

[dpb]

for i = 1:31
  [Y, I] = min((latS-latG(i)).^2 + (lonS-lonG(i)).^2);
  disp(I)                                             
  ...

" %Prints indices of the matched coordinates"

But this is only sequentially through the loop for each element in turn, you haven't saved the found location; each pass overwrites the previous so indeed when the loop finishes all you have is the last iteration.

The most "deadahead" solution given the existing code would be

N=31;
Y=zeros(N,1); I=Y;     % preallocate
for i = 1:N
  [Y(i), I(i)] = min((latS-latG(i)).^2 + (lonS-lonG(i)).^2);
  ...

[Brandon Bush]

It didnt quite work. It gave me indices that didnt coordinate with those represented by I

[dpb]

I guess I misinterpreted what you were asking for...I thought the I was a "pick 'em" vector to select a subset, not a predefined set of indices. Your problem is outlined in revised Answer...