# Converting a date to a calendar quarter

I have a list that includes dates. I need to convert each date to be the last day of the quarter that it's in. So for example I want {2013,7,1,0,0,0} to become {2013,9,30,0,0,0}. Actually I don't need the zero's. I was trying to do this with a rule, but ran into problems. I wanted a rule like: 7,_ -> 9,30. Further I was going to try to insert alternatives into this with something like 7,_ |8,_ |9,_ -> 9,30.

Is there a way to write a rule to handle this? Or, for this specific problem is there a better way to convert these dates to quarter end dates?

An example of a row of data is: {{2009,5,1,0,0,0},"TYAU145A", 92468., 0.5, 46234.}.

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Creating function endq :-

endq = DateList[{#1, 1 + 3 Ceiling[#2/3], 0}] &;

endq @@ {2013, 1, 1, 0, 0, 0}


{2013, 3, 31, 0, 0, 0.}

For example, with data :-

a = {{{2009, 5, 1, 0, 0, 0}, "TYAU145A", 92468., 0.5, 46234.},
{{2012, 8, 12, 0, 0, 0}, "TYAU145A", 92468., 0.5, 46234.},
{{2001, 12, 9, 0, 0, 0}, "TYAU145A", 92468., 0.5, 46234.}};

{endq @@ #1, ##2} & @@@ a


{{{2009, 6, 30, 0, 0, 0.}, "TYAU145A", 92468., 0.5, 46234.}, {{2012, 9, 30, 0, 0, 0.}, "TYAU145A", 92468., 0.5, 46234.}, {{2001, 12, 31, 0, 0, 0.}, "TYAU145A", 92468., 0.5, 46234.}}

Alternatively, using a rule :-

qrule = {y_, m_, __} :> DateList[{y, 1 + 3 Ceiling[m/3], 0}];

{# /. qrule, ##2} & @@@ a

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I'm still working on your "endq" solution. I don't understand how it works. I see how it gets the year and the month if I understand how the slots work. How does it get the last day of the month? Although I'm really not sure how any of it works. I assumed endq @@ replaces List with the endq function. I can understand how one head is replaced by another head, say Plus @@. I'm really not seeing what happens. Using FullForm or Hold didn't help me very much, probably because I'm not that facile with them either. Any suggestions? – Mitchell Kaplan Dec 3 '13 at 21:24
@MitchellKaplan - Hi, I'm using Apply (@@) to pick up the numbered slot arguments, e.g. {#1, #2} & @@ {2013, 6, 30}. The month end calculation is done by DateList : setting the day to zero steps back a day, so DateList[{2013, 7, 0}] finds the last day of June. Likewise DateList[{2013, 14, 0}] finds the last day of January. – Chris Degnen Dec 3 '13 at 22:15
Thanks, I've learned a lot from this, although I'll have to play with slots some more to fully get it. – Mitchell Kaplan Dec 3 '13 at 22:44
quarterfy[{y_, m_, _, z___}] :=
Switch[m,
1 | 2 | 3, {y, 3, 31, z},
4 | 5 | 6, {y, 6, 30, z},
7 | 8 | 9, {y, 9, 30, z},
10 | 11 | 12, {y, 12, 31, z}
]

quarterfy@{2013, 7, 1, 0, 0, 0}
(* {2013, 9, 30, 0, 0, 0}  *)

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