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Why Doesn't DatePattern Work with Position?

Gregory Lypny
Posted 9 years ago

Hi everyone,

I have a list of strings called myStrings, and there is exactly one element containing "7 November 2009".

I can pick off that element using StringMatchQ as

StringMatchQ[myStrings, 
 DatePattern[{"DayShort", " ", "MonthName", " ", "Year"}]]

But if I use Position

Position[myStrings, 
 DatePattern[{"DayShort", " ", "MonthName", " ", "Year"}]]

it returns {}. What am I doing wrong?

Gregory
POSTED BY: Gregory Lypny
2 Replies
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Xavier Roy
Xavier Roy, WOLFRAM
Posted 9 years ago

Hi Gregory,

I am not sure to understand either why it returns an empty list. Perhaps when using strings as list elements in Position, one should use a different pattern construction. But I am not sure why this would be the case, so I do not know. I would be interested if anyone has an idea.

Here is a way that seems to solve the issue. It is not very nice but it works fine:

Position[myStrings, 
        _?(StringMatchQ[#, DatePattern[{"DayShort", "MonthName", "Year"}, " "]] &), Heads -> False]

The Heads -> False avoids Position to test the head of myStrings, which would result otherwise in a warning from StringMatchQ.

Regards, Xavier
POSTED BY: Xavier Roy
Gregory Lypny
Gregory Lypny
Posted 9 years ago
POSTED BY: Gregory Lypny
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