How to count occurrences of Friday 13th
Clash Royale CLAN TAG#URR8PPP
9
$begingroup$
I would like to find a function that will count the number of times Friday 13th happens in a particular calendar year.
Does anybody have any hints ?
Thank you
date-and-time
edited Mar 5 at 2:20
J. M. is slightly pensive♦
98.9k10311467
$endgroup$
add a comment |
9
$begingroup$
I would like to find a function that will count the number of times Friday 13th happens in a particular calendar year.
Does anybody have any hints ?
Thank you
date-and-time
edited Mar 5 at 2:20
J. M. is slightly pensive♦
98.9k10311467
$endgroup$
1
$begingroup$
I fell into a delightful rabbit hole of day-counting algorithms on Wikipedia. I wanted to leave a link to the Doomsday algorithm for mental calculation of the day of the week, for fun: Doomsday rule on Wiki.
$endgroup$
– MarcoB
Mar 4 at 19:54
$begingroup$
Wolfram Challenges.
$endgroup$
– J. M. is slightly pensive♦
Mar 5 at 2:21
$begingroup$
Sounds like one for the code golf boys and girls
$endgroup$
– Strawberry
Mar 5 at 13:05
$begingroup$
Oh, of course they did it already: codegolf.stackexchange.com/questions/69510/…
$endgroup$
– Strawberry
Mar 5 at 13:11
add a comment |
9
9
9
$begingroup$
I would like to find a function that will count the number of times Friday 13th happens in a particular calendar year.
Does anybody have any hints ?
Thank you
date-and-time
edited Mar 5 at 2:20
J. M. is slightly pensive♦
98.9k10311467
$endgroup$
I would like to find a function that will count the number of times Friday 13th happens in a particular calendar year.
Does anybody have any hints ?
Thank you
date-and-time
date-and-time
edited Mar 5 at 2:20
J. M. is slightly pensive♦
98.9k10311467
edited Mar 5 at 2:20
J. M. is slightly pensive♦
98.9k10311467
edited Mar 5 at 2:20
J. M. is slightly pensive♦
98.9k10311467
edited Mar 5 at 2:20
J. M. is slightly pensive♦
98.9k10311467
edited Mar 5 at 2:20
J. M. is slightly pensive♦
98.9k10311467
98.9k10311467
asked Mar 4 at 19:23
user63250
1
$begingroup$
I fell into a delightful rabbit hole of day-counting algorithms on Wikipedia. I wanted to leave a link to the Doomsday algorithm for mental calculation of the day of the week, for fun: Doomsday rule on Wiki.
$endgroup$
– MarcoB
Mar 4 at 19:54
$begingroup$
Wolfram Challenges.
$endgroup$
– J. M. is slightly pensive♦
Mar 5 at 2:21
$begingroup$
Sounds like one for the code golf boys and girls
$endgroup$
– Strawberry
Mar 5 at 13:05
$begingroup$
Oh, of course they did it already: codegolf.stackexchange.com/questions/69510/…
$endgroup$
– Strawberry
Mar 5 at 13:11
add a comment |
1
$begingroup$
I fell into a delightful rabbit hole of day-counting algorithms on Wikipedia. I wanted to leave a link to the Doomsday algorithm for mental calculation of the day of the week, for fun: Doomsday rule on Wiki.
$endgroup$
– MarcoB
Mar 4 at 19:54
$begingroup$
Wolfram Challenges.
$endgroup$
– J. M. is slightly pensive♦
Mar 5 at 2:21
$begingroup$
Sounds like one for the code golf boys and girls
$endgroup$
– Strawberry
Mar 5 at 13:05
$begingroup$
Oh, of course they did it already: codegolf.stackexchange.com/questions/69510/…
$endgroup$
– Strawberry
Mar 5 at 13:11
1
1
$begingroup$
I fell into a delightful rabbit hole of day-counting algorithms on Wikipedia. I wanted to leave a link to the Doomsday algorithm for mental calculation of the day of the week, for fun: Doomsday rule on Wiki.
$endgroup$
– MarcoB
Mar 4 at 19:54
$begingroup$
I fell into a delightful rabbit hole of day-counting algorithms on Wikipedia. I wanted to leave a link to the Doomsday algorithm for mental calculation of the day of the week, for fun: Doomsday rule on Wiki.
$endgroup$
– MarcoB
Mar 4 at 19:54
$begingroup$
Wolfram Challenges.
$endgroup$
– J. M. is slightly pensive♦
Mar 5 at 2:21
$begingroup$
Wolfram Challenges.
$endgroup$
– J. M. is slightly pensive♦
Mar 5 at 2:21
$begingroup$
Sounds like one for the code golf boys and girls
$endgroup$
– Strawberry
Mar 5 at 13:05
$begingroup$
Sounds like one for the code golf boys and girls
$endgroup$
– Strawberry
Mar 5 at 13:05
$begingroup$
Oh, of course they did it already: codegolf.stackexchange.com/questions/69510/…
$endgroup$
– Strawberry
Mar 5 at 13:11
$begingroup$
Oh, of course they did it already: codegolf.stackexchange.com/questions/69510/…
$endgroup$
– Strawberry
Mar 5 at 13:11
add a comment |
2 Answers
2
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oldest
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10
$begingroup$
Select[
Table[DateObject@2019, m, 13, m, 12],
DateString[#, "DayName"] === "Friday" &
]
Day: Fri 13 Sep 2019,Day: Fri 13 Dec 2019
countFri13[year_Integer]:=Length @ Select[
Table[DateObject@year, m, 13, m, 12],
DateString[#, "DayName"] === "Friday" &
]
answered Mar 4 at 19:35
Kuba♦Kuba
107k12210533
$endgroup$
add a comment |
13
$begingroup$
I worked on this problem in 2015. Here is part on my notebook from that time.
A not so good algorithm.
friday13th[year_Integer] :=
Select[DayName[#] === Friday &] @
DateRange[DateObject[year, 1, 13], DateObject[year, 12, 13], 1, "Month"]
A good algorithm.
friday13th[year_Integer] :=
Select[DayName[#] === Friday &] @ Table[DateObject[year, i, 13], i, 12]
A better algorithm.
friday13th[year_Integer] :=
Select[DayName[#] === Friday &] @ Array[DateObject[year, #, 13] &, 12]
Using the better algorithm, I got (at the time I created the notebook)
friday13th @ 2014
friday13th @ 2015
And for this year, I get
friday13th @ 2019
answered Mar 4 at 19:52
m_goldbergm_goldberg
88k872199
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add a comment |
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2 Answers
2
active
oldest
votes
2 Answers
2
active
oldest
votes
active
oldest
votes
active
oldest
votes
10
$begingroup$
Select[
Table[DateObject@2019, m, 13, m, 12],
DateString[#, "DayName"] === "Friday" &
]
Day: Fri 13 Sep 2019,Day: Fri 13 Dec 2019
countFri13[year_Integer]:=Length @ Select[
Table[DateObject@year, m, 13, m, 12],
DateString[#, "DayName"] === "Friday" &
]
answered Mar 4 at 19:35
Kuba♦Kuba
107k12210533
$endgroup$
add a comment |
10
$begingroup$
Select[
Table[DateObject@2019, m, 13, m, 12],
DateString[#, "DayName"] === "Friday" &
]
Day: Fri 13 Sep 2019,Day: Fri 13 Dec 2019
countFri13[year_Integer]:=Length @ Select[
Table[DateObject@year, m, 13, m, 12],
DateString[#, "DayName"] === "Friday" &
]
answered Mar 4 at 19:35
Kuba♦Kuba
107k12210533
$endgroup$
add a comment |
10
10
10
$begingroup$
Select[
Table[DateObject@2019, m, 13, m, 12],
DateString[#, "DayName"] === "Friday" &
]
Day: Fri 13 Sep 2019,Day: Fri 13 Dec 2019
countFri13[year_Integer]:=Length @ Select[
Table[DateObject@year, m, 13, m, 12],
DateString[#, "DayName"] === "Friday" &
]
answered Mar 4 at 19:35
Kuba♦Kuba
107k12210533
$endgroup$
Select[
Table[DateObject@2019, m, 13, m, 12],
DateString[#, "DayName"] === "Friday" &
]
Day: Fri 13 Sep 2019,Day: Fri 13 Dec 2019
countFri13[year_Integer]:=Length @ Select[
Table[DateObject@year, m, 13, m, 12],
DateString[#, "DayName"] === "Friday" &
]
answered Mar 4 at 19:35
Kuba♦Kuba
107k12210533
answered Mar 4 at 19:35
Kuba♦Kuba
107k12210533
answered Mar 4 at 19:35
Kuba♦Kuba
107k12210533
answered Mar 4 at 19:35
Kuba♦Kuba
107k12210533
107k12210533
add a comment |
add a comment |
13
$begingroup$
I worked on this problem in 2015. Here is part on my notebook from that time.
A not so good algorithm.
friday13th[year_Integer] :=
Select[DayName[#] === Friday &] @
DateRange[DateObject[year, 1, 13], DateObject[year, 12, 13], 1, "Month"]
A good algorithm.
friday13th[year_Integer] :=
Select[DayName[#] === Friday &] @ Table[DateObject[year, i, 13], i, 12]
A better algorithm.
friday13th[year_Integer] :=
Select[DayName[#] === Friday &] @ Array[DateObject[year, #, 13] &, 12]
Using the better algorithm, I got (at the time I created the notebook)
friday13th @ 2014
friday13th @ 2015
And for this year, I get
friday13th @ 2019
answered Mar 4 at 19:52
m_goldbergm_goldberg
88k872199
$endgroup$
add a comment |
13
$begingroup$
I worked on this problem in 2015. Here is part on my notebook from that time.
A not so good algorithm.
friday13th[year_Integer] :=
Select[DayName[#] === Friday &] @
DateRange[DateObject[year, 1, 13], DateObject[year, 12, 13], 1, "Month"]
A good algorithm.
friday13th[year_Integer] :=
Select[DayName[#] === Friday &] @ Table[DateObject[year, i, 13], i, 12]
A better algorithm.
friday13th[year_Integer] :=
Select[DayName[#] === Friday &] @ Array[DateObject[year, #, 13] &, 12]
Using the better algorithm, I got (at the time I created the notebook)
friday13th @ 2014
friday13th @ 2015
And for this year, I get
friday13th @ 2019
answered Mar 4 at 19:52
m_goldbergm_goldberg
88k872199
$endgroup$
add a comment |
13
13
13
$begingroup$
I worked on this problem in 2015. Here is part on my notebook from that time.
A not so good algorithm.
friday13th[year_Integer] :=
Select[DayName[#] === Friday &] @
DateRange[DateObject[year, 1, 13], DateObject[year, 12, 13], 1, "Month"]
A good algorithm.
friday13th[year_Integer] :=
Select[DayName[#] === Friday &] @ Table[DateObject[year, i, 13], i, 12]
A better algorithm.
friday13th[year_Integer] :=
Select[DayName[#] === Friday &] @ Array[DateObject[year, #, 13] &, 12]
Using the better algorithm, I got (at the time I created the notebook)
friday13th @ 2014
friday13th @ 2015
And for this year, I get
friday13th @ 2019
answered Mar 4 at 19:52
m_goldbergm_goldberg
88k872199
$endgroup$
I worked on this problem in 2015. Here is part on my notebook from that time.
A not so good algorithm.
friday13th[year_Integer] :=
Select[DayName[#] === Friday &] @
DateRange[DateObject[year, 1, 13], DateObject[year, 12, 13], 1, "Month"]
A good algorithm.
friday13th[year_Integer] :=
Select[DayName[#] === Friday &] @ Table[DateObject[year, i, 13], i, 12]
A better algorithm.
friday13th[year_Integer] :=
Select[DayName[#] === Friday &] @ Array[DateObject[year, #, 13] &, 12]
Using the better algorithm, I got (at the time I created the notebook)
friday13th @ 2014
friday13th @ 2015
And for this year, I get
friday13th @ 2019
answered Mar 4 at 19:52
m_goldbergm_goldberg
88k872199
answered Mar 4 at 19:52
m_goldbergm_goldberg
88k872199
answered Mar 4 at 19:52
m_goldbergm_goldberg
88k872199
answered Mar 4 at 19:52
m_goldbergm_goldberg
88k872199
88k872199
add a comment |
add a comment |
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1
$begingroup$
I fell into a delightful rabbit hole of day-counting algorithms on Wikipedia. I wanted to leave a link to the Doomsday algorithm for mental calculation of the day of the week, for fun: Doomsday rule on Wiki.
$endgroup$
– MarcoB
Mar 4 at 19:54
$begingroup$
Wolfram Challenges.
$endgroup$
– J. M. is slightly pensive♦
Mar 5 at 2:21
$begingroup$
Sounds like one for the code golf boys and girls
$endgroup$
– Strawberry
Mar 5 at 13:05
$begingroup$
Oh, of course they did it already: codegolf.stackexchange.com/questions/69510/…
$endgroup$
– Strawberry
Mar 5 at 13:11