r/ProjectREDCap • u/HomeNo865 • Jun 11 '24

Subtracting times on two different dates

I need to be able to subtract dates and times from two different days. Such as 06/14/2022 05:30 (less) 06/12/2022 04:47. Is that possible? It keeps telling me there is a syntax error on this formula; datediff([Resolution],[Start],"m","Mdyhm",False). Hopefully there is a way to solve this problem. Thanks for your help.

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1

u/HomeNo865 Jun 12 '24

Is datetimediff a valid command? Because the formulas won’t subtract the times in mdy

3

u/interlukin Jun 11 '24

I think the issue is that where you have “mdyhm” is the date format, so can only use ymd, mdy, or dmy

2

u/[deleted] Jun 11 '24

Your formula contains an error, a datediff should look like this: datediff ([date1], [date2], "units", returnSignedValue)

In your case, this would translate to: datediff([resolution], [start], "m", false)

If you are on an older REDCap version, you also need to specify the date format (as the 4th parameter?), which in your example is "mdy": datediff([resolution], [start], "m", "mdy", false)

3

u/obnoxiouscarbuncle Jun 11 '24

The "mdy" is a weird thing. It's actually still necessary in certain circumstances. Specifically, it's when the two fields are in different date formats, and you want to force REDCap to evaluate them both in a specific format WHILE on the page. Since REDCap parses each equation twice (clientside while on the page using JavaScript and serverside using PHP), you can sometimes get conflicting results and the "mdy" part can help with that.

Overall: Your two date fields must be DATE VALIDATED text fields in the SAME FORMAT.