Efficient way to find the first value that exceeds limits in a 1column array

Hello,

I have a matrix with only one column of measures (eye coordinates on the screen on the x-axis). The code needs to find the first value that goes beyond a specific limit.

In other words, the matrix starts with values in the range 120:140 (which indicate the position of the eye is approximately on the center of the screen)Then, the values can be either (< 120) or (> 140) (indicating the eye moved towards the left or the right). I need to find the (i-row,1) position in which the values go beyond the limit of 120 or 140 (I cannot know in advance the direction of the eye).

________

i.e the raw data in my matrix could be something like that:

EyeRawData(:,1)= [130,135,125,136,131,...,128,121,116,90,76,65,65,54,65,70]
or
EyeRawData(:,1)= [130,135,125,136,131,...,139,142,156,170,190,191,189,187,190]

I need to count trough the entire rawdata 'how many rows it takes to get to the value 121 (or 142)'. And return EyeRawData (i,1)

___________

So, at the moment, I have written something like this:

l= length(EyeRawData);

for i=1:l
  if (EyeRawData(i,l) > 140) || (EyeRawData(i,l) < 120)
     position= i;
     break
  end
end

Can you please tell me whether this is a correct way of doing it or there are more efficient ways?

thank you very much

Giulia

Answer 1

[Star Strider]

My approach would be to use the find function:

ERDI = find( (EyeRawData > 140) | (EyeRawData < 120) );

returning the indices of ‘EyeRawData’ that correspond to either condition.

[Matt J]

To find the first occurrence, modify as

position = find( (EyeRawData > 140) | (EyeRawData < 120) , 1 );

[Star Strider]

Thank you Matt J. By the time I read through the question and experimented with it, I forgot about the ‘first value’ part.

[Giulia]

Thank you very much Star Strider and Matt J. This is very useful and I can get loads of other important info with just one line.

Best

Giulia

[Star Strider]

My pleasure!