How to get the rows and columns from a matrix which do not fall into particular criteria?

Hello,

My data comprises of a matrix.

% Data1 = 25000 x 30 double

After running some lines of code I got my Data2 (from Data1 using logical indexing etc) which is now

% Data2 = 10000 x 30 double

However I also want to do some statistics on the rest 15000 x 30 dataset. I guess it's quite simple but I can't figure out how to get this 15000 x 30 matrix from Data1. After doing logical indexing etc I got Data2, how to get the remaining matrix which do not fall into my particular criteria for Data2 i.e, 15000x30? Thank you

Answer 1

[Dyuman Joshi]

Use negation on the logical indexing -

x = 0:0.01:10;
y = [sin(x); cos(x)];
%Get columns of y in which
%first row is less than or equal to -0.25
idx = y(1,:)<=-0.25;
data1 = y(:,idx)

data1 = 2×297

-0.2555 -0.2652 -0.2748 -0.2844 -0.2940 -0.3035 -0.3131 -0.3225 -0.3320 -0.3414 -0.3508 -0.3601 -0.3694 -0.3787 -0.3880 -0.3971 -0.4063 -0.4154 -0.4245 -0.4335 -0.4425 -0.4515 -0.4604 -0.4692 -0.4780 -0.4868 -0.4955 -0.5042 -0.5128 -0.5213 -0.9668 -0.9642 -0.9615 -0.9587 -0.9558 -0.9528 -0.9497 -0.9466 -0.9433 -0.9399 -0.9365 -0.9329 -0.9293 -0.9255 -0.9217 -0.9178 -0.9137 -0.9096 -0.9054 -0.9011 -0.8968 -0.8923 -0.8877 -0.8831 -0.8783 -0.8735 -0.8686 -0.8636 -0.8585 -0.8534

%Get the data which doesn't fall into that category
data = y(:,~idx)

data = 2×704

0 0.0100 0.0200 0.0300 0.0400 0.0500 0.0600 0.0699 0.0799 0.0899 0.0998 0.1098 0.1197 0.1296 0.1395 0.1494 0.1593 0.1692 0.1790 0.1889 0.1987 0.2085 0.2182 0.2280 0.2377 0.2474 0.2571 0.2667 0.2764 0.2860 1.0000 1.0000 0.9998 0.9996 0.9992 0.9988 0.9982 0.9976 0.9968 0.9960 0.9950 0.9940 0.9928 0.9916 0.9902 0.9888 0.9872 0.9856 0.9838 0.9820 0.9801 0.9780 0.9759 0.9737 0.9713 0.9689 0.9664 0.9638 0.9611 0.9582

[Zhou Ci]

It gives me error

Data3 = Data1(:, ~Data2)

The logical indices in position 2 contain a true value outside of the array bounds.

[Dyuman Joshi]

You have to use the logical indexing, not the data itself. I have assigned the logical indexing to the variable idx and then used the variable.

What is the criteria you are using?

[Zhou Ci]

Here is my complete code:

% Data1 = 25000X30
Lat=Data1(:,1);
Lon=Data1(:,2);
land = shaperead('landareas', 'UseGeoCoords', true);
land_flags = zeros(length(Lat),1);
for i = 1 : size(land,1)
    Lat_land = land(i).Lat;
    Lon_land = land(i).Lon;
    in1 = inpolygon(Lat(:),Lon(:),Lat_land,Lon_land);
    land_flags = land_flags + in1;
end

Data1 = Data1(land_flags == 0,:);
Data2 = real(Data1);   % 10000x30 

I also want the remaining 'Data3' (15000x30) from the Data1 dataset.

[Dyuman Joshi]

Lat=Data1(:,1);
Lon=Data1(:,2);
land = shaperead('landareas', 'UseGeoCoords', true);
land_flags = zeros(length(Lat),1);
for i = 1 : size(land,1)
    Lat_land = land(i).Lat;
    Lon_land = land(i).Lon;
    in1 = inpolygon(Lat(:),Lon(:),Lat_land,Lon_land);
    land_flags = land_flags + in1;
end

idx = land_flags == 0:
Data1 = Data1(idx,:);
Data2 = real(Data1);   % 10000x30 

Data3 = Data1(~idx,:)