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

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Zhou Ci 2023-3-16

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https://ww2.mathworks.cn/matlabcentral/answers/1929590-how-to-get-the-rows-and-columns-from-a-matrix-which-do-not-fall-into-particular-criteria

评论： Dyuman Joshi 2023-3-16

采纳的回答： Dyuman Joshi

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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

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Answer 1

Dyuman Joshi 2023-3-16

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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

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Zhou Ci 2023-3-16

在 MATLAB Online 中打开

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 2023-3-16

在 MATLAB Online 中打开

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,:) 