Converting an entire MATLAB table column from epoch to datetime format

Question

R 2022-2-14

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1649270-converting-an-entire-matlab-table-column-from-epoch-to-datetime-format

评论： Seth Furman 2022-2-15

I am currently reading in two files, both of that consist of Epoch time. To use timetable in MATLAB, I am required to have the format of time as datetime. I am currently trying to convert an entire "time" column into datetime from epoch. However, when I try to use the suggested function I get the following error. This is my first time properly using MATLAB so any help would be appreciated! Thank you :)

Error using datetime (line 588)

Input data must be one numeric matrix when converting from a different date/time representation.

Error in DataAnalysis_Ver1 (line 13)

y = datetime(x, 'ConvertFrom','posixtime','TimeZone','Asia/Tokyo');

%reading and plotting the Ring Data
sleeponData = readtable('file1.csv');
sleeponTimestamp = sleeponData(:,"time");
sleeponTimestamparray = table2array(sleeponTimestamp);
sleeponSportRaw = table2array(sleeponData(:,"sportRaw"));
sleeponSportRaw = 5000*sleeponSportRaw;
%converting epoch time to datetime
rows = height(sleeponData); 
for row = 1:rows 
    x = sleeponData(row,1);
    y = datetime(x, 'ConvertFrom','posixtime','TimeZone','Asia/Tokyo');
    sleeponData.time(row) = y;
end
%reading the pillow
data = importdata('file2.csv');
data(:,2) = [];
tabledata = array2table(data);
%get rid of the second column (contains messages)
%pillowTime = array2table(data(:,1));
%synchronizing the timestamp
%new = synchronize(sleeponData, data, 'secondly','linear');
new = synchronize(sleeponData, tabledata);
disp(new);

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Answer 1

Seth Furman 2022-2-14

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1649270-converting-an-entire-matlab-table-column-from-epoch-to-datetime-format#answer_895940

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It looks like we just need to change

x = sleeponData(row,1);

to the following

x = sleeponData{row,1};

Note the use of curly braces-{} instead of parentheses-(). sleeponData is a table, so indexing with parentheses-() will return another table with the specified data, while curly braces-{} will return the data at the specified row and column indices.

See the following page in our documentation for more information.

Access Data in Tables - Extract Data from Specified Rows and Variables

If that does not fix the error, please attach an example file (for instance file1.csv) and/or include a concrete example of a timestamp you are trying to convert into a datetime.

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R 2022-2-15

matlab.csv

Thank you for your help! I used the curly braces but I still got an error.

i have attached the picture of the error when I ran the code

Seth Furman 2022-2-15

在 MATLAB Online 中打开

Please see Walter's response. The loop is not needed in this case, only

y = datetime(sleeponData.time, 'ConvertFrom','posixtime','TimeZone','Asia/Tokyo');
sleeponData.time = y;

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Answer 2

Walter Roberson 2022-2-15

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1649270-converting-an-entire-matlab-table-column-from-epoch-to-datetime-format#answer_896360

在 MATLAB Online 中打开

%reading and plotting the Ring Data
sleeponData = readtable('file1.csv');
sleeponTimestamp = sleeponData(:,"time");
sleeponTimestamparray = table2array(sleeponTimestamp);
sleeponSportRaw = table2array(sleeponData(:,"sportRaw"));
sleeponSportRaw = 5000*sleeponSportRaw;
%converting epoch time to datetime
%no loop needed
y = datetime(sleeponData.time, 'ConvertFrom','posixtime','TimeZone','Asia/Tokyo');
sleeponData.time = y;
%reading the pillow
data = importdata('file2.csv');
data(:,2) = [];
tabledata = array2table(data);
%get rid of the second column (contains messages)
%pillowTime = array2table(data(:,1));
%synchronizing the timestamp
%new = synchronize(sleeponData, data, 'secondly','linear');
new = synchronize(sleeponData, tabledata);
disp(new);