MATLAB: I need to know how to select values from a 2×365 array

columnhelpmatrixmatrix manipulation

hey i have a 2×365 array and i know that if you use column_1= data (1:365) to select the data in the first column but how would i input it to get all of the data for the secound column

Best Answer

No, if you have a 2 x 365 array, then column_1 = data(1:365) would get you the first 182 full columns and the first row of the 183'rd column as well. To get the first column you would use data(:,1) which will get you a 2 x 1 vector. The second column would be data(:,2) which would get you a 2 x 1 vector.

I suspect you are looking for rows rather than columns. row_1 = data(1,:); row_2 = data(2,:); and each of those would be 1 x 365.

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MATLAB: How to plot no of events

ExcludeIt = isnan(YourData(:,2));
OkayDates = YourData(~ExcludeIt,1);
Okay_vec = datevec(OkayDates);
minyear = min(Okay_vec(:,1));
idx = (Okay_vec(:,1)-minyear) * 12 + Okay_vec(:,2);  %year and month
counts = accumarray(idx(:), 1);
numentry = size(counts,1);
bar_dates = datenum([minyear * ones(numentry,1), (1:numentry).', ones(numentry,1)]);
bar(bar_dates, counts)
datetick('x', 'mmm YYYY')

and you might want to look at http://www.mathworks.com/matlabcentral/answers/93388-how-can-i-rotate-the-axis-tick-labels-in-2-d-and-3-d

MATLAB: How to find the coordinate of the intersection multiple lines

Interesting Friday afternoon problem!

The solution is reasonably straightforward, although not immediately obvious. The ‘Row’ designations correspond to the rows of ‘x’ and ‘y’, since that is the easiest way to refer to them. (The lines do not intersect in the original plot, so I assume the idea is to see where they would intersect if they were extended.)

First, estimate the parameters of each line:

for k = 1:size(x,1)
    B(:,k) = [x(k,:)' ones(2,1)] \ y(k,:)';                         % Parameters
end

Then determine the intersections:

for k1 = 1:size(B,2)
    for k2 = 1:size(B,2)
        XY(k1,k2,:) = [-B(1,[k1 k2])' [1;1]] \ B(2,[k1 k2])';       % Intersections
    end
end
X = XY(:,:,1)
Y = XY(:,:,2)

Then tabulate the intersections:

Names = sprintfc('Row_%d',1:4);
XInt = table(X(:,1),X(:,2),X(:,3),X(:,4),'VariableNames',Names,'RowNames',Names)
YInt = table(Y(:,1),Y(:,2),Y(:,3),Y(:,4),'VariableNames',Names,'RowNames',Names)
XInt =
             Row_1     Row_2    Row_3     Row_4 
             ______    _____    ______    ______
    Row_1       NaN        9         7    5.3333
    Row_2         9      NaN       7.2     4.875
    Row_3         7      7.2       NaN    6.1667
    Row_4    5.3333    4.875    6.1667       NaN
    
YInt =
             Row_1     Row_2    Row_3     Row_4 
             ______    _____    ______    ______
    Row_1       NaN      10          8    6.3333
    Row_2        10     NaN        8.8      7.25
    Row_3         8     8.8        NaN    4.6667
    Row_4    6.3333    7.25     4.6667       NaN

And plot them:

xv = linspace(0,15);
Ym = B(1,:)'*xv + B(2,:)';
figure
plot(xv,Ym)
ylim([0 15])
grid
legend(Names, 'Location','SE')

Best Answer

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MATLAB: How to plot no of events

MATLAB: How to find the coordinate of the intersection multiple lines

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