You need to understand two things. Variable name and variable values are different things. You don’t have any year or date value in your data instead. What you have is years stored as variable or column names instead of having them as values. Moreover what is stored under each variable (read column) is some other measure.
If I am able to put it correctly, you have data reshaping problems. Values should never be stored as column names. What is correct is that year should be column names and its values like 2018 2019 etc should have been stored in that column.
Now proceed like this, click all year columns in data pane/window and click pivot. This will result in a longer data with two columns in lieu of all year columns – pivot col names and pivot values. Rename first one as year. Second one as metric.
Now you can create a calculate field on year column. This will result in creation of a date field as desired.
If you are still unable to do it, upload your excel/csv file on a drive and paste a link, i will demonstrate you.
Good luck
P.s. transposing your data in Excel itself may solve your problem directly, if you can do it.
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