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convert date to datenum import from excel

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ErikJ
ErikJ 2018-7-17
评论： ErikJ 2018-7-19
hello
I want to import a simple excel file to matlab and convert the column with dates from text to numeric values. The problem is that the rule convert does not show up as an alternativ. I can only replace things. Would be very glad if someone could help.

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Adam Danz
Adam Danz 2018-7-17
编辑：Adam Danz 2018-7-17
I agree that readtable() is the better option but if you decide to stick with the import tool, here's an idea.
In the dropdown menu under your variable name 'dag' where it currently says "Number" in your screenshot, select a date and time option. This will convert your timestamps to datetime format. After importing, you can use datenum() to convert them to double if desired.
Here's a screen shot with a different data set.
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Walter Roberson
Walter Roberson 2018-7-17
When you click to generate, it should have created importfile.m
Adam Danz
Adam Danz 2018-7-17
Yeah, that might be the problem. After you select datetime you'll need to re-generate the importfile() function so the new version accounts for the new format.

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Walter Roberson
Walter Roberson 2018-7-17
We recommend using readtable() instead. With new enough MATLAB, it can help to use detectImportOptions() with readtable()
ErikJ
ErikJ 2018-7-19
I solved the problem now. Thanks! Now when I have imported the data I calculate new values based on the old. Now I would very much like to add this new values as a new row (=one new value per column) and save this in the excel file (overwrite) without changing the formatting. How can i do this?
Thanks in advance
Erik
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Adam Danz
Adam Danz 2018-7-19
编辑：Adam Danz 2018-7-19
doc xlswrite()
Read about the inputs and how to use this function. There's even an example that shows you how to insert data into specific cells of the spreadsheet. I was about to type up a quick demo but Matlab's documentation covers it. The best way to learn is by digging into the documentation. If you get stuck, come back.
It would be wise to make a copy of your data as you poke around with this function in case you accidentally overwrite your data.
ErikJ
ErikJ 2018-7-19
Ok thanks. I'll read about xlswrite()

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