# Remove all rows of an array based on a value in a column, and also remove all rows that have the same values as this row in other columns

2 views (last 30 days)
Jason on 9 Aug 2022
Commented: Jason on 9 Aug 2022
Hi, I have the centroids (x,y) of e.g 3 objects as shown in the pic:
I also have an array of the centroid locations (x,y) of each point and then calculate the distance of every other point from that point. Columns 1, 2 are (x,y) of an object, 3rd and 4th columns are coordinates of other objects, and column 5 is their seperation
M =
15.88 18.43 15.88 18.43 0
15.88 18.43 33.48 14.99 17.94
15.88 18.43 53.49 37.71 42.27
33.48 14.99 15.88 18.43 17.94
33.48 14.99 33.48 14.99 0
33.48 14.99 53.49 37.71 30.27
53.49 37.71 15.88 18.43 42.27
53.49 37.71 33.48 14.99 30.27
53.49 37.71 53.49 37.71 0
what I want to do is e.g. select a distance i.e. d=40, and then remove all rows in which column 5 (= their seperation) is above this value AND also any other row that has the same values in col 1 & 2. i.e. so to completely remove any object that is close to another object.
This is my attempt:
% Create another matrix where the condition is met
M1=M(M(:,5) < d, :);
disp('after')
M1
% Create conditions
TF1 = M(:,1)==M1(:,1)
TF1 = M(:,2)==M1(:,2)
% combine them
TFall = TF1 & TF2
% remove
M(TFall,:) = []
Jason on 9 Aug 2022
Matt, it was towards the same goal yes, but I realised that finding the distance of all objects and simply finding rows where this is below a set value doesn't quite work - but it did answer the main question - how to find distance of all objects!. Yes I could have added this problem in a comment there too, but this is more of a general matrix manipulation problem (i.e. use column 5 to flag the values in columns 1 & 2 and then put remove all rows that have these col 1& 2 values. I thought as its a different Matlab problem it would be easier to search for as well so I created a new thread.

Bruno Luong on 9 Aug 2022
M = [
15.88 18.43 15.88 18.43 0
15.88 18.43 33.48 14.99 17.94
15.88 18.43 53.49 37.71 42.27
33.48 14.99 15.88 18.43 17.94
33.48 14.99 33.48 14.99 0
33.48 14.99 53.49 37.71 30.27
53.49 37.71 15.88 18.43 42.27
53.49 37.71 33.48 14.99 30.27
53.49 37.71 53.49 37.71 0 ];
xy=M(:,1:2)
xy = 9×2
15.8800 18.4300 15.8800 18.4300 15.8800 18.4300 33.4800 14.9900 33.4800 14.9900 33.4800 14.9900 53.4900 37.7100 53.4900 37.7100 53.4900 37.7100
M(ismember(xy,xy(M(:,5)>40,1:2),'rows'),:)=[]
M = 3×5
33.4800 14.9900 15.8800 18.4300 17.9400 33.4800 14.9900 33.4800 14.9900 0 33.4800 14.9900 53.4900 37.7100 30.2700
##### 1 CommentShow NoneHide None
Jason on 9 Aug 2022
Thankyou, I modified it slightly to remove the rows with the last coloumn as zero and it worked beautifully
TF1 = M(:,5)==0;
M(TF1,:) = []

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