I am using Matlab 2012a.
I have an array of k cells (say 1000). I need to find the 5 lowest values of this array and need to do an average of those values in X and Y.
Anyone has an idea how to do that?
3 Answers
Assuming you have arrays X and Y, and you want to find the five lowest Y values:
[m mi] = sort(Y);
lowest5index = mi(1:5);
lowest5Y = Y(lowest5index);
lowest5X = X(lowest5index);
meanYlowest5 = mean(lowest5Y);
meanXlowest5 = mean(lowest5X);
Explanation:
The sort command with two output parameters returns both the sorted array (in m) and the indices in the original array (mi). The first five indices mi(1:5) correspond to the five lowest values. Taking the mean of these values for both X and Y will do what we want. If I didn't understand your problem statement, please clarify your question and I will take another shot at it.
3 Comments
Vissenbot
Yeah, sorry I wasn't clear enough. I need to find the 5 lowest values in Y, and then make an average of both the X and Y of these 5 points! Your technique was quite interesting though! I'll keep that trick in mind if it comes in handy!
Floris
My technique does exactly what you are asking for... I have edited the code to make it even clearer. If it still doesn't work for you, you need to explain your data structure more clearly.
Vissenbot
Okay, this worked. I thought that by sorting them, you would modify the X values. I misunderstood. Thanks for the help! :D
How about doing a sort of your array from lowest value to the highest and then selecting the 5 first values. Those will be the 5 min values of your array. Then perform a mean of those 5 values.
This might not be the most memory efficient way of doing this but for just 1000 values it will get the job done!
Hope it helps!
Comments
use minmaxselection MATLAB MEX package, which has been specially optimized for this problem:
a = [2,3,4,7,56,4,21, 64, -2];
mink(a, 2)
<< ans =
<< -2 2
mink(a,4)
<< ans =
<< -2 2 3 4
"find highest k values". This seems useful.