# Loop through date time heart rate data

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Ross Thompson il 23 Apr 2021
Risposto: Eric Sofen il 7 Mag 2021
I have a large csv with lots of days worth of continuous heartrate data which can be seen below. I have been splitting the data up into 2 groups, each an hour in length, to calculate the p value between the 2 groups. I want to create a loop which will continuously move the split point (30th point in this case) of the groups forward by 1 datapoint and then calculte the new p value for the new split. I want to then plot these p-values over the whole timeframe. How would i go about doing this?
Timestamp Heart rate
2021-02-01 12:00:00 76.0
2021-02-01 12:02:00 89.0
2021-02-01 12:04:00 86.0
2021-02-01 12:06:00 89.0
2021-02-01 12:08:00 82.0
2021-02-01 12:10:00 87.0
2021-02-01 12:12:00 87.0
2021-02-01 12:14:00 84.0
2021-02-01 12:16:00 81.0
2021-02-01 12:18:00 81.0
A = data.HeartRate(1:30);
B = data.HeartRate(31:60);
[h, p, ci] = ttest2(A,B)
C = data.HeartRate(2:31);
D = data.HeartRate(32:61);
[h, p, ci] = ttest2(C,D)
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### Risposte (1)

Eric Sofen il 7 Mag 2021
Can you assume that the data is always sampled uniformly every 2 minutes? That can simplify things, but the code below should be general.
Also, I'd recommend using a timetable for this, as it will make time subscripting easier.
The timerange function will help with selecting the data chunks.
% Cook up some synthetic data
HeartRate = 60+randi(20,[30*24,1]);
data = timetable(HeartRate,'TimeStep',minutes(2),'StartTime',datetime(2021,05,07));
data.Properties.DimensionNames{1} = 'Timestamp';
windowStart = data.Timestamp(1);
% Need to figure out where to stop so there's enough data for the last set
% of moving windows.
windowEnd = data.Timestamp(end)-hours(2);
numWindows = height(data(timerange(windowStart,windowEnd),:));
% Preallocate the p-value timetable. Split the confidence interval into 2
% vars. It could also be one 2-element wide var.
tp = array2timetable(nan(numWindows,4),'RowTimes',data.Timestamp(1:numWindows),'VariableNames',{'h','p','ciLow','ciHigh'});
for ii = 1:numWindows
start = data.Timestamp(ii);
A = data.HeartRate(timerange(start, start+hours(1)));
B = data.HeartRate(timerange(start+hours(1),start+hours(2)));
[h, p, ci] = ttest2(A,B);
tp.h(ii) = h;
tp.p(ii) = p;
tp{ii,["ciLow","ciHigh"]} = ci';
end
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