MATLAB: Extracting and plotting max/min values from timeseries

MATLABmaxmeanminplottime series

I have a time series with continuous measurements of pH. The measurements are every 5 minutes, and the timeseries is a total of 13 days.

I want to find and plot the max and min value for each day, where the max and min values are based on 24 observations of a mean pH/hour.

So far I've been able to get the mean pH per hour, but I don't know how to find the max/min values from these and then plot as a continuous time series.

This is what I've done so far to find the mean pH for every hour:

dnv = [time];
dv6 = datevec(dnv);                                     % Date vector matrix, 6 columns
dn4 = datenum([dv6(:,1:4) repmat([0 0],size(dv6,1),1)]);
[Du,~,di] = unique(dn4, 'stable');
Means = accumarray(di, pH, [], @mean);              % Creating means for every hour
Out = [datevec(Du)  Means];                         % Output separated columns, date time mean
de = datetime(Out(:,1:6));                          % Merged date and time back into 1 column

So, how do I find the max and min values with the associated date and time for plotting?

Best Answer

Better take advantage of table format and splitapply function.

tbl = readtable('data.csv');
tbl.day  = day(tbl.Date);
tbl.hour = hour(tbl.Date);
 
[Group, hourTbl] = findgroups(tbl(:, {'day', 'hour'}));
hourTbl.mean = splitapply(@nanmean, tbl.pH, Group);
[Group, dayTbl]  = findgroups(hourTbl(:, 'day'));
dayTbl.max = splitapply(@max, hourTbl.mean, Group);
dayTbl.min = splitapply(@min, hourTbl.mean, Group);

Related Solutions

MATLAB: I am working with tthe3 files, and I have csv hourly data for a whole year. I need to get the maximum of a certain value for each month and plot them and also performing addition to another value for each day and getting the max and min day

I've imported 8th column (3:end rows) to MATLAB and found max value of each month

plot(DNIWm2)
days = [0 31 28 31 30 31 30 31 31 30 31 30 31];
[maxValue, maxHour] = deal(zeros(12,1));
hour = 0;
hold on
for i = 1:12;
    hour = hour + days(i)*24;
    data = DNIWm2( hour+1 : hour+days(i+1)*24 );    % extracting data of a current month
    [maxValue(i), H] = max( data );                 % local max value and hour
    maxHour(i) = H + hour;                          % hour in data
    plot([hour hour], [0 1000],'-ok')       % plot first/last hour of a month
end
plot(maxHour,maxValue,'-or')
hold off

MATLAB: For loop using unique values

Indeed using find would be madness. For the record, find is over used by beginners and is rarely needed. For that matters, for loop are also overused and are also not needed in this case.

There are many ways to do this:

Using groupsummary:

maxdischarge = groupsummary(yourmatrix(:, 4), yourmatrix(:, 2), 'max');

Using splitapply:

[group, month] = findgroups(yourmatrix(:, 2));  %may not be needed if the month column is integers from 1 to 12
maxdischarge = splitapply(@max, yourmatrix(:, 4), group);  %maxdischarge(i) corresponds to month(i)

Using old fashioned accumarray:

[month, ~, group] = unique(yourmatrix(:, 2));  %works like findgroups, with different order of output. Again may not be needed
maxdischarge = accumarray(yourmatrix(:, 4), group, [], @max);

Or even using a loop:

maxdischarge = zeros(12, 1)
for month = 1:12
    maxdischarge = max(yourmatrix(yourmatrix(:, 2) == month, 4));
end

Note that I would recommend that you convert your matrix into a table:

t = array2table(yourmatrix, 'VariableNames', {'Day', 'Month', 'Year', 'Discharge'});

In which case, you definitively should use groupsummary:

groupsummary(t, 'Month', 'max', 'Discharge');  %calculate max of discharge grouped by month

Even better would be to convert the first 3 columns into a datetime array:

t = table(datetime(yourmatrix(:, 3), yourmatrix(:, 2), yourmatrix(:, 1)), yourmatrix(:, 4), 'VariableNames', {'Date', 'Discharge'});
groupsummary(t, 'Date', 'monthofyear', 'max', 'Discharge')

Best Answer

Related Solutions

MATLAB: I am working with tthe3 files, and I have csv hourly data for a whole year. I need to get the maximum of a certain value for each month and plot them and also performing addition to another value for each day and getting the max and min day

MATLAB: For loop using unique values

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