How do I find a specific x values in an array(?) of x,y locations?

I'm able to create a matrix of x, y values ,

coordinates = [1,2; 3,4; 10,5; 4,5];

and use find(x), to search in the array,

find(coordinates == 10);

however once I attempt to use a bigger matrix this function doesnt seem to work and I dont understand why,

find(locations==143.4955);

returns an empty matrix but I know there are x values with 143.4955 in the matrix, can anyone help me?

Answer 1

[Chunru]

% Now you have posted your data:
load('location array.mat')
whos

  Name              Size            Bytes  Class     Attributes

  ans               1x43               86  char                
  locations      2670x2             21360  single              

% Your data is 2670x2
locations

locations = 2670×2

3.4017 263.0466 3.4017 263.0466 3.7207 87.7808 3.7207 87.7808 3.9423 249.8393 3.9423 249.8393 4.1351 96.5079 4.1351 96.5079 4.1892 83.5233 4.1892 83.5233

% floating point inside computer may not be exact
plot(locations(:,1)); hold on; plot(locations(:,2))

% Your data has values (in both columns) close to 143.4955
% In searching the closest points, you have to specify a suitable tolerance: 1e-4 below

% Search along the 1st column (you may have different criterion)
idx = find(abs(locations(:,1) - 143.4955) < 1e-4)

idx = 3×1

1284 1285 1286

locations(idx, :)

ans = 3×2

143.4955 158.7091 143.4955 158.7091 143.4955 158.7091

[Drew Ellington]

this is just returning the same empty column vector.....I need to return the index of the x values at 143.4955.....

[Chunru]

See the data with your posted data.