DateSelect

DateSelect[list,crit]

picks out all dates datei of a list for which crit[datei] is True.

DateSelect[int,crit]

returns all dates within the DateInterval int for which crit[datei] is True.

DateSelect[crit]

represents an operator form of DateSelect that can be applied to an expression.

Details

  • DateSelect is typically used to filter out dates that satisfy a criterion, such as falling in a specific month or day of the week.
  • In DateSelect[list,crit], crit is a Boolean expression, typically composed of date element tests, such as #Month==8 or #DayName==Monday.
  • DateSelect supports all date elements available in DateValue, including "Year", "Month", "DayName" and "Week", expressed as a named Slot such as #Year, #Month, etc.
  • For DateInterval inputs, DateSelect returns a list of dates using the calendar granularity specified by the interval.

Examples

open allclose all

Basic Examples  (4)

Select all dates in May within a given list of dates:

Get all dates within the 8th week of the year:

Get all Wednesdays within a given date interval:

Select any instance of February 4, as well as all Thursdays within the given range:

Find the 4th day of each odd-numbered month:

Scope  (2)

Selection criteria are typically reference date elements using Slot expressions but may use any Boolean criteria:

DateSelect extracts element values without converting calendars or changing time zones:

The value of #Day is determined by the calendar associated with the input date:

The value of #Hour is checked without accounting for differences in time zones:

To select dates using a standardized time zone, first use TimeZoneConvert:

Applications  (1)

DateSelect can be used for scheduling purposes, picking out dates that match a given pattern, such as the first Monday in any given month:

Properties & Relations  (1)

DateSelect[dates,crit] is equivalent to Select[dates,DateValue[#,elem]==value&]

Possible Issues  (1)

Not all calendars include all elements as selection criteria:

Dates may be converted to a different calendar prior to selection using CalendarConvert:

Neat Examples  (3)

On the Gregorian calendar, the 13th day of the month is a Friday more frequently than any other day of the week:

Create a criterion for US presidential elections (first Tuesday after the first Monday in November every 4 years):

Use the criterion to find all presidential election days in a 20-year period:

A Gregorian century never begins on a Sunday, regardless of whether it starts on year 1 or year zero:

Wolfram Research (2020), DateSelect, Wolfram Language function, https://reference.wolfram.com/language/ref/DateSelect.html.

Text

Wolfram Research (2020), DateSelect, Wolfram Language function, https://reference.wolfram.com/language/ref/DateSelect.html.

BibTeX

@misc{reference.wolfram_2021_dateselect, author="Wolfram Research", title="{DateSelect}", year="2020", howpublished="\url{https://reference.wolfram.com/language/ref/DateSelect.html}", note=[Accessed: 04-August-2021 ]}

BibLaTeX

@online{reference.wolfram_2021_dateselect, organization={Wolfram Research}, title={DateSelect}, year={2020}, url={https://reference.wolfram.com/language/ref/DateSelect.html}, note=[Accessed: 04-August-2021 ]}

CMS

Wolfram Language. 2020. "DateSelect." Wolfram Language & System Documentation Center. Wolfram Research. https://reference.wolfram.com/language/ref/DateSelect.html.

APA

Wolfram Language. (2020). DateSelect. Wolfram Language & System Documentation Center. Retrieved from https://reference.wolfram.com/language/ref/DateSelect.html