MATLAB time duration in milliseconds from an excel file - matlab

Question

I am making a Matlab program that uses data from an excel file designated from an open file dialog.
[filename, pathname] = uigetfile({'*.xlsx','Excel Files(*.xlsx)'; '*.txt','Txt Files(*.txt)'}, 'Pick a file');
FilePath = append(pathname,filename);
opts = detectImportOptions(FilePath, "ReadVariableNames", false);
opts = setvartype(opts, 1, 'char');
data = readtable(FilePath, opts);
table = data(:,1);
Now the code is like this.
enter image description here
After that, as you see the date is saved as string.
But what I really want to find is time difference (duration) in milliseconds.
The raw data looks like this:
enter image description here
A column and C column has the same time, so I want to only use A column data.
Please help a newbie with this!! I appreciate!

Answer 1

Problem resolved.
I share my code to help other people suffering the same problem.
Please leave comments if things can be more simplified.
Importing an Excel file to analyze
% Clean the memory and the code previously running
clc;
clear all;
close all;
% Sampling frequency of the acquired data
fs = 1e2; % Sampling Frequency - this can be found on LabView code.
Ts = 1/fs; % Sampling Interval
%Importing data from an excel file
[filename, pathname] = uigetfile({'*.xlsx','Excel Files(*.xlsx)'; '*.txt','Txt Files(*.txt)'}, 'Pick a file');
FilePath = append(pathname,filename);
[fPath ,fName, fExt] = fileparts(FilePath);
a. To find "Time duration" from the file
opts = spreadsheetImportOptions("NumVariables", 1);
% Specify sheet and range
opts.Sheet = "sheet1";
opts.DataRange = "A2";
% Specify column names and types
opts.VariableNames = "Time";
opts.VariableTypes = "datetime";
% Specify file level properties
opts.ImportErrorRule = "omitrow";
opts.MissingRule = "omitrow";
% Specify variable properties
opts = setvaropts(opts, "Time", "InputFormat", 'mm:ss.SSS');
tTable = readtable(FilePath, opts, "UseExcel", false);
tArray = table2array(tTable);
% Calculating time duration
tArray = tArray - tArray(1);
% Coverting to seconds
time = milliseconds(tArray)*1e-3;
% Clear temporary variables
clear opts;
% Discarding data if time difference is too big
ii = size(time(:,1));
k = 0;
disp('Now removing error data elements');
for i = 1:1:ii(1)-1
a = time(i);
b = time(i+1);
if (b-a)>0.5 && k==0
k=i+1;
fprintf('Elements from %d seconds will be removed. (%dth element)\n', time(k),k);
for j = ii(1):-1:k
if rem(j,10)==0
fprintf('%dth element is removed... \n',j);
end
time(j) = [];
end
break % Break the loop after removing error data
end
end
disp('Time table is set.');
clearvars -except filename FilePath fs pathname time k ii Ts fName

Answer 2

I created a similar excel file and I found the time columns are read as a char. So, what I did is get the index of those columns and convert it to datatime. After that, looks that it is working. Hopefully, this works.
% Define the excel file name (can be the path)
ExcelFile = 'demo_stackflow.xlsx';
% Get the options for that sheet and preserving the variable name
opts = detectImportOptions(ExcelFile,'Sheet','Sheet1',...
"VariableNamingRule","preserve")
% Get the idx where the variable is a char (In this case col 1 and 3)
CharVars = opts.VariableNames(contains(opts.VariableTypes,'char'));
% Convert the char columns to datetime
opts = setvaropts(opts,CharVars,'Type',"datetime");
% Get the data
data = readtable(ExcelFile, opts)
% Print the 1st column to see if the data type of the column is
% datetime
T = data(:,1)