You need a "day" portion in there too.

So do

MID([srting field],  1, 3) + "/1/" + MID([string field], 5,4)

Make a Calculated Field using DATEPARSE like

DATEPARSE("MMM-yyyy",[yourDateField])

If DATEPARSE can be made to work correctly, then inserting the Day value explicitly should not be required.

(Note I said "if" and "should"     )

If you need help with various date formats and the DATEPARSE function, here is a helpful link.

http://kb.tableau.com/articles/knowledgebase/understanding-the-dateparse-function

Regards,

Rody

Could you post a sample of the data? Maybe 10 rows with the field formatted exactly has you get it in Tableau?

I tested by making a 3-line Excel that looks like

Month

'Apr-2011

'Nov-2013

and that worked fine with DATEPARSE as given here.   But the relevant thing is what does your data look like when it goes into Tableau?

Okay yes that helps, but a screen shot is not the same thing as a data sample.

Please look at the attached, to be sure that this works.

One thing you should also know about DATEPARSE is that it is very Case Sensitive in its use of the formatting string. That is by ICU convention.  So you can't just mix and match upper and lower case for the Y and M bits.

Jonathan,

You are getting 'nulls' because the dateparse formula is converting the 'contents' of the date column(s) you have in your data. For dateparse to work, you need all the date strings in one column so that when you choose to dateparse that column, it actually converts those strings to date type:

Your best bet here may be to reshape the data using the add-in Installing the Tableau Add-In for Reshaping Data in Excel | Tableau Software

and bring all date strings into one column and then choose that column to parse the date, so that you data looks something like this: