How can I summarize datapoints (coordinates which are closer than 0.2 meter for example), keep only the mean values of these groups and delete the others?

Its my first matlab use: I need to delete some data points on a grid which are at almost the same coordinate. There shouldnt be missing data so i want to take the mean value of every group of data with same coordinates. Do i need to create a new matrix because of the size of the data set? And how can i write a generalized code to formulate: 'take all points closer then 0.2m and replace with mean value of these points? Thanks in advance for your ideas

[KSSV]

Closer than 0.2m from what?

[Jan]

@Sabine Haase: Are you looking for a set of clusters, which classify your data points? See https://en.wikipedia.org/wiki/Cluster_analysis

[Sabine Haase]

closer than 0.2m from each other, or the next point in line

[Sabine Haase]

@Jan Simon: Yes and then replace these clusters with each mean value. Unfortunately I don't know how to express it in matlab

Answer 1

[Sindhuja Parimalarangan]

Looking at the big picture, I understand that you essentially want to delete data points at almost the same coordinate locations.

Workaround 1

This looks like a " hierarchical clustering with complete linkage " problem. You can set the relevant "distance" and "linkage" properties.

Workaround 2

You can also look into " kmeans " where each cluster of points will have an assigned centroid (like the mean). You can extract the cluster indices and cluster centroid locations as output and delete other elements from the matrix.

You can delete elements from a matrix like this:

A =

     1     2     3
     4     5     6
     7     8     9

>> A(:,2) = []

A =

     1     3
     4     6
     7     9

Workaround 3

If you would like to be specific and not use built-in clustering functions, you can write a function to do the following:

1. For a given element in a matrix (input argument for the function), store the surrounding elements you want to consider.

2. Calculate distances of the element with the surrounding ones.

3. Delete element (as shown above) if distance is less than 0.2

You can use " bsxfun " to apply the this custom function to every element of the matrix.