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Week of the Year, and Day of the Week/Month/Year

Problem

Given a date, you need to find out what week of the year, day of the week, day of the month, or day of the year that the date falls on.

Solution

We'll use our good all friend SRFI 19, and by using date->string, with the appropriate conversion specifiers, we'll get what we want:

(require (lib "19.ss" "srfi"))

(let ((today (current-date)))
  (values
   (date->string today)
   (date->string today
                 "Week No.: ~V, day: (~w of week) (~d of month) 
                 (~j of year)")))

Note: there are several other specifiers that you can pass to date->string.

If what you need is the actual numbers, then you can extract this information from the date instance yourself:

(require (lib "19.ss" "srfi"))

(let ((today (current-date)))
  (values
   (date->string today)
   ;; `1' means `Monday' is the first day of the week:
   (date-week-number today 1)
   (date-week-day today)
   (date-day today)
   (date-year-day today)))

Discussion

If you are wondering what to use when you are using the Epoch (seconds) representation of the given date, then you should consider transforming your number of seconds to date, and then use this recipe. See recipe TimeEpochToTime to pass from seconds to dates.

See Also

SRFI 19: Time Data Types and Procedures

Comments here

-- FranciscoSolsona - 05 May 2004