Converting an entire MATLAB table column from epoch to datetime format

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R
R 2022-2-14
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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回答（2 个）

Seth Furman
Seth Furman 2022-2-14
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.
  2 个评论
R
R 2022-2-15
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
Seth Furman 2022-2-15
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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Walter Roberson
Walter Roberson 2022-2-15
%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);

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