Issue with table data creating strings and recognising as numbers

I'm working on my minor disseration project - this isn't a necessary step at all, I'm doing it as an attempt to get extra credit. I used MATLAB for my third year disseration last year and imported data in a similar way and did not have this issue. Imported data from excel.

I know why the date isn't working as it isn't a conventional number (a way to convert this would be very helpful also? without editing the excel file if possible) but I don't understand why the others are being processed as strings.

I tried using str2double to fix this but my graph still is empty in terms of numbers so the issue is MATLAB not recognising what I'm giving it as numbers.

I have attached the .mat files.

Any help would be appreciated.

function MAVENdata
a = open('10-9-17 cmes.mat');
b = open('4-8-16 cme.mat');
% import data and convert into an array
c = table2array(a.cmes100917);
d = table2array(b.Untitled);

datec=c(:,1));
nTxc=c(:,2));
nTyc=c(:,3));
nTzc=c(:,4));
nTc=c(:,5));

dated=d(:,1));
nTxd=d(:,2));
nTyd=d(:,3));
nTzd=d(:,4));
nTd=d(:,5));

subplot(2,1,1)
plot(datec, nTxc,'k'); hold on;
plot(datec, nTyc,'r'); hold on;
plot(datec, nTzc,'g'); hold on;
plot(datec, nTc,'b'); hold on;
ylabel('MAG (nT)');
xlabel('Timescale');
grid on
hold off;
end

[Walter Roberson]

open() of aa mat file brings up aa variable import dialog if II recall correctly . load() would seem to be more appropriate .

Answer 1

[Cris LaPierre]

What version of MATLAB are you using? If possible, I'd recommend you take advantage of some of the newer features. In particular, I'd recommend datetimes and tables. I modified your mat files back to spreadsheets. Here's how I would implement your code (and it automatically handles the dates).

opts = detectImportOptions('cmes040816.xlsx');
opts = setvartype(opts,'timetagyyyyMMddTHHmmssSSS','datetime');
opts = setvaropts(opts,'timetagyyyyMMddTHHmmssSSS','InputFormat','uuuu-MM-dd''T''HH:mm:ss.SSS');

data16 = readtable('cmes040816.xlsx',opts);
data17 = readtable('cmes100917.xlsx',opts);

data16.Properties.VariableNames = {'date','nTx','nTy','nTz','nT'};
data17.Properties.VariableNames = {'date','nTx','nTy','nTz','nT'};

hold on
plot(data16.date, data16.nTx,'k');
plot(data16.date, data16.nTy,'r');
plot(data16.date, data16.nTz,'g');
plot(data16.date, data16.nT,'b');
hold off;

ylabel('MAG (nT)');
xlabel('Timescale');
grid on

[Cris LaPierre]

Also, note that you have an extra closing parentheses when you are extracting data from your array.

datec=c(:,1));
...

[Hannah Joyce]

using 2018b (just updated this morning), tried running this and I get the error

Error using matlab.io.ImportOptions/getNumericSelection (line
468)
Unknown variable name: 'timetagyyyyMMddTHHmmssSSS'.

Error in matlab.io.ImportOptions/setvartype (line 271)
                    selection =
                    opts.getNumericSelection(selection);

Error in MAVENdata (line 4)
opts =
setvartype(opts,'timetagyyyyMMddTHHmmssSSS','datetime');

[Hannah Joyce]

tried removing the 'timetag' stuff and got

Undefined variable "date16" or class "date16.date".

[Cris LaPierre]

It is not recognizing the variable name for the first column. What are your column headers? From the data you shared, they appeared to be

• timetagyyyyMMddTHHmmssSSS
• mag_magnetic_field_mso_xnT
• mag_magnetic_field_mso_ynT
• mag_magnetic_field_mso_znT
• mag_mso_magnitudenT

That's ok. You don't have to use the actual name. You can use indexing instead. Just modify the setvartype lines of code to

opts = detectImportOptions('cmes040816.xlsx');
opts = setvartype(opts,1,'datetime');
opts = setvaropts(opts,1,'InputFormat','uuuu-MM-dd''T''HH:mm:ss.SSS');

data16 = readtable('cmes040816.xlsx',opts);
data17 = readtable('cmes100917.xlsx',opts);

[Cris LaPierre]

re date16.date - that was a typo. It should be data16.date. I've corrected the code above.

[Hannah Joyce]

super late response (I've been very busy) but thank you very much!!!

Answer 2

[Brian Hart]

Hi Hannah,

Try replacing, for example,

nTxc=c(:,2));

with

nTxc=a.cmes100917(:,2).mag_magnetic_field_mso_xnT;

(I used tab completion rather than typing the whole field name).

This gives me a nTxc variable of type double, and with

plot(nTxc,'k')

I get