Find data between min and max

Hello there,

I have used the two functions islocalmin and islocalmax to find minimum and maximum points in my data.

TFmin = islocalmin(task, 'MinProminence',10) 
TFmax = islocalmax(task, 'MinProminence',10)


plot(time_s,task, time_s (TFmin),task(TFmin),'r*')
hold on
plot(time_s,task,time_s(TFmax),task(TFmax),'b*')

I have identified different points as you can see in the attached plots, and I ended up with 10 points.

Now, I need to create two variables (task + time_s) repressing the data that lies in between each minimum and maximum point.

For example (see attached pic):

I need extract the exact date of time and task between the points:

1 and 2

3 and 4

5 and 6

7 and 8

9 and 10

And also the opposite:

2 and 3

4 and 5

6 and 7

8 and 9

Any advice or help would be much appreciated.

Thank you

Answer 1

[Star Strider]

An accumarray call can do that relatively easily:

D = load('test.mat');
task = D.task;
time_s = D.time_s;

TFmin = islocalmin(task, 'MinProminence',10); 
TFmax = islocalmax(task, 'MinProminence',10);
MinIdx = find(TFmin);
MaxIdx = find(TFmax);
Idx = sort([MinIdx; MaxIdx]);

IdxCell = accumarray(Idx(1:numel(Idx)-1), (1:numel(Idx)-1).', [], @(x){Idx(x):Idx(x+1)});   % Cell Array Of Index Ranges
IdxRng = find(cellfun(@(x)~isempty(x), IdxCell));                                           % Index Ranges
GetData = @(x) [time_s(IdxCell{IdxRng(x)}),  task(IdxCell{IdxRng(x)})];                     % Function To Retrieve Data Easily

Get1 = GetData(1);                                                                          % Get First Set
X1 = Get1(:,1);
Y1 = Get1(:,2);

Get3 = GetData(3);                                                                          % Get Third Set
X3 = Get3(:,1);
Y3 = Get3(:,2);

figure
plot(time_s,task, time_s (TFmin),task(TFmin),'r*')
hold on
plot(time_s,task,time_s(TFmax),task(TFmax),'b*')
plot(X1, Y1, '.r')                                                                          % Plot First Set
plot(X3, Y3, '.g')                                                                          % Plot Third Set
hold off

Producing this example plot:

Thius code recovers all of the intervals, not only the ascending ones, so choose the odd-numbered arguments to ‘GetData’.

[Ahmed Alalawi]

Amazing !

[Star Strider]

Thank you!

Answer 2

[Jeremy]

Something like this?

t = linspace(0,2*pi,201);
y = sin(t);
plot(t,y,'LineWidth',2)
grid on
hold on
minid = find(islocalmin(y));
maxid = find(islocalmax(y));
[~,d] = min([minid maxid])
switch d
    case 1
        data_id = minid:1:maxid;
    case 2
        data_id = maxid:1:minid;
end
t_int = t(data_id);
y_int = y(data_id);
plot(t_int,y_int,'r--','LineWidth',2)