Days between dates

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Revision as of 16:15, 15 October 2019 by Steenslag (talk | contribs) (→‎{{header|Ruby}}: Added Ruby)
Days between dates is a draft programming task. It is not yet considered ready to be promoted as a complete task, for reasons that should be found in its talk page.
Task

Calculate the number of days between two dates. Date input should be of the form YYYY-MM-DD.

Motivation

To demonstrate one of the numerous ways this can be done.


AWK

<lang AWK>

  1. syntax: GAWK -f DAYS_BETWEEN_DATES.AWK

BEGIN { 

   regexp = "^....-..-..$" # YYYY-MM-DD
   main("1969-12-31","1970-01-01","builtin has bad POSIX start date")
   main("1970-01-01","2038-01-19","builtin has bad POSIX stop date")
   main("1970-01-01","2019-10-02","format OK")
   main("1970-01-01","2019/10/02","format NG")
   main("1995-11-21","1995-11-21","identical dates")
   main("2019-01-01","2019-01-02","positive date")
   main("2019-01-02","2019-01-01","negative date")
   main("2019-01-01","2019-03-01","non-leap year")
   main("2020-01-01","2020-03-01","leap year")
   exit(0)

} function main(date1,date2,comment, d1,d2,diff) { 

   printf("\t%s\n",comment)
   d1 = days_builtin(date1)
   d2 = days_builtin(date2)
   diff = (d1 == "" || d2 == "") ? "error" : d2-d1
   printf("builtin %10s to %10s = %s\n",date1,date2,diff)
   d1 = days_generic(date1)
   d2 = days_generic(date2)
   diff = (d1 == "" || d2 == "") ? "error" : d2-d1
   printf("generic %10s to %10s = %s\n",date1,date2,diff)

} function days_builtin(ymd) { # use gawk builtin 

   if (ymd !~ regexp) { return("") }
   if (ymd < "1970-01-01" || ymd > "2038-01-18") { return("") } # outside POSIX range
   gsub(/-/," ",ymd)
   return(int(mktime(sprintf("%s 0 0 0",ymd)) / (60*60*24)))

} function days_generic(ymd, d,m,y,result) { # use Python formula 

   if (ymd !~ regexp) { return("") }
   y = substr(ymd,1,4)
   m = substr(ymd,6,2)
   d = substr(ymd,9,2)
   m = (m + 9) % 12
   y = int(y - int(m/10))
   result = 365*y + int(y/4) - int(y/100) + int(y/400) + int((m*306+5)/10) + (d-1)
   return(result)

} </lang>

Output:
    builtin has bad POSIX start date
builtin 1969-12-31 to 1970-01-01 = error
generic 1969-12-31 to 1970-01-01 = 1
    builtin has bad POSIX stop date
builtin 1970-01-01 to 2038-01-19 = error
generic 1970-01-01 to 2038-01-19 = 24855
    format OK
builtin 1970-01-01 to 2019-10-02 = 18171
generic 1970-01-01 to 2019-10-02 = 18171
    format NG
builtin 1970-01-01 to 2019/10/02 = error
generic 1970-01-01 to 2019/10/02 = error
    identical dates
builtin 1995-11-21 to 1995-11-21 = 0
generic 1995-11-21 to 1995-11-21 = 0
    positive date
builtin 2019-01-01 to 2019-01-02 = 1
generic 2019-01-01 to 2019-01-02 = 1
    negative date
builtin 2019-01-02 to 2019-01-01 = -1
generic 2019-01-02 to 2019-01-01 = -1
    non-leap year
builtin 2019-01-01 to 2019-03-01 = 59
generic 2019-01-01 to 2019-03-01 = 59
    leap year
builtin 2020-01-01 to 2020-03-01 = 60
generic 2020-01-01 to 2020-03-01 = 60

Erlang

<lang erlang>

-module(daysbetween). -export([between/2,dateToInts/2]).

% Return Year or Month or Date from datestring dateToInts(String, POS) -> 

 list_to_integer( lists:nth( POS, string:tokens(String, "-") ) ).

% Alternative form of above % dateToInts(String,POS) -> % list_to_integer( lists:nth( POS, re:split(String ,"-", [{return,list},trim]) ) ).

% Return the number of days between dates formatted "2019-09-30" between(DateOne,DateTwo) -> 

 L = [1,2,3],
 [Y1,M1,D1] =  [ dateToInts(DateOne,X) || X <- L],
 [Y2,M2,D2] =  [ dateToInts(DateTwo,X) || X <- L],
 GregOne = calendar:date_to_gregorian_days(Y1,M1,D1),
 GregTwo = calendar:date_to_gregorian_days(Y2,M2,D2),
 GregTwo - GregOne.

</lang>

Output:

erlang shell: 

30> c(daysbetween).
c(daysbetween).
{ok,daysbetween}
31> daysbetween:between("2019-01-01", "2019-09-30").
daysbetween:between("2019-01-01", "2019-09-30").
272

Factor

Factor supports the addition and subtraction of timestamps and durations with the time+ and time- words. <lang factor>USING: calendar calendar.parser kernel math prettyprint ;

days-between ( ymd-str ymd-str -- n )
   [ ymd>timestamp ] bi@ time- duration>days abs ;

"2019-01-01" "2019-09-30" days-between . "2016-01-01" "2016-09-30" days-between .  ! leap year</lang>

Output:
272
273

Go

<lang go>package main

import ( 

   "fmt"
   "log"
   "time"

)

const layout = "2006-01-02" // template for time.Parse

// Parameters assumed to be in YYYY-MM-DD format. func daysBetween(date1, date2 string) int { 

   t1, err := time.Parse(layout, date1)
   check(err)
   t2, err := time.Parse(layout, date2)
   check(err)
   days := int(t1.Sub(t2).Hours() / 24)
   if days < 0 {
       days = -days
   }
   return days

}

func check(err error) { 

   if err != nil {
       log.Fatal(err)
   }

}

func main() { 

   date1, date2 := "2019-01-01", "2019-09-30"
   days := daysBetween(date1, date2)
   fmt.Printf("There are %d days between %s and %s\n", days, date1, date2)

   date1, date2 = "2015-12-31", "2016-09-30"
   days = daysBetween(date1, date2)
   fmt.Printf("There are %d days between %s and %s\n", days, date1, date2)

}</lang>

Output:
There are 272 days between 2019-01-01 and 2019-09-30
There are 274 days between 2015-12-31 and 2016-09-30

Lua

This uses os.difftime to compare two Epoch times. Not to be used with dates before 1970. <lang lua>SECONDS_IN_A_DAY = 60 * 60 * 24

-- Convert date string as YYYY-MM-DD to Epoch time. function parseDate (str) 

 local y, m, d = string.match(str, "(%d+)-(%d+)-(%d+)")
 return os.time({year = y, month = m, day = d})

end

-- Main procedure io.write("Enter date 1: ") local d1 = parseDate(io.read()) io.write("Enter date 2: ") local d2 = parseDate(io.read()) local diff = math.ceil(os.difftime(d2, d1) / SECONDS_IN_A_DAY) print("There are " .. diff .. " days between these dates.")</lang>

Output:
Enter date 1: 1970-01-01
Enter date 2: 2019-10-02
There are 18171 days between these dates.

Perl

Would not reinvent this wheel. <lang perl>use feature 'say'; use Date::Calc qw(Delta_Days);

say Delta_Days(2018,7,13, 2019,9,13); # triskaidekaphobia say Delta_Days(1900,1,1, 2000,1,1); # a century say Delta_Days(2000,1,1, 2100,1,1); # another, with one extra leap day say Delta_Days(2020,1,1, 2019,10,1); # backwards in time say Delta_Days(2019,2,29, 2019,3,1); # croaks</lang>

Output:
427
36524
36525
-92
Date::Calc::PP::Delta_Days(): Date::Calc::Delta_Days(): not a valid date at Days_between_dates line 10

Perl 6

Dates are first class objects in Perl 6 and may have arithmetic in days done directly on them. <lang perl6>say Date.new('2019-09-30') - Date.new('2019-01-01');

say Date.new('2019-03-01') - Date.new('2019-02-01');

say Date.new('2020-03-01') - Date.new('2020-02-01');

say Date.new('2029-03-29') - Date.new('2019-03-29');

say Date.new('2019-01-01') + 90;

say Date.new('2020-01-01') + 90;

say Date.new('2019-02-29') + 30;

CATCH { default { .message.say; exit; } };</lang> 

272
28
29
3653
2019-04-01
2020-03-31
Day out of range. Is: 29, should be in 1..28

Python

<lang python>

  1. !/usr/bin/python

import sys

Difference between two dates = g(y2,m2,d2) - g(y1,m1,d1) 

   Where g() gives us the Gregorian Calendar Day
   Inspired  by discussion at:
   https://stackoverflow.com/questions/12862226/the-implementation-of-calculating-the-number-of-days-between-2-dates

def days( y,m,d ): 

  input year and month are shifted to begin the year in march
 m = (m + 9) % 12 
 y = y - m/10

  with (m*306 + 5)/10 the number of days from march 1 to the current 'm' month 
 result = 365*y + y/4 - y/100 + y/400 + (m*306 + 5)/10 + ( d - 1 )
 return result

def diff(one,two): 

 [y1,m1,d1] = one.split('-')
 [y2,m2,d2] = two.split('-')
 # strings to integers
 year2 = days( int(y2),int(m2),int(d2))
 year1 = days( int(y1), int(m1), int(d1) )
 return year2 - year1

if __name__ == "__main__": 

 one = sys.argv[1]
 two = sys.argv[2]
 print diff(one,two)

</lang>

Output:
python days-between.py 2019-01-01 2019-09-30
272

REXX

Works with: Regina REXX

bare bones version

Programming note:   the   B   (Base)   an option for the   date   BIF which indicates to compute the number of
days since the beginning of the Gregorian calendar,   and   I   which is the option that indicates the date is in
the   ISO   (International Standards Organization standard 8601:2004)   format. <lang rexx>/*REXX program computes the number of days between two dates in the form of YYYY-MM-DD */ parse arg $1 $2 . /*get 2 arguments (dates) from the C.L.*/ say abs( date('B',$1,"I") - date('B',$2,"I") ) ' days between ' $1 " and " $2 

                                                /*stick a fork in it,  we're all done. */</lang>
output   when using the inputs of:     2019-10-02   2000-01-01 
6848  days between  2019-10-02  and  2000-01-01

supports more variations

This REXX version supports more variations in the date format   (allows a single digit month and/or day), as well as
allowing a single asterisk   (*)   to be used for a date   (which signifies that the current date is to be used).

Commas   (,)   are inserted into numbers where appropriate.

Also, more informative error messages are generated. <lang rexx>/*REXX program computes the number of days between two dates in the form of YYYY-MM-DD */ parse arg $.1 $.2 _ . 1 . . xtra /*obtain two arguments from the C.L. */ if $.1=='*' then $.1= date("I") /*obtain current date if it's an *. */ if $.2=='*' then $.2= date("I") /* " " " " " " " */ parse var $.1 yr.1 '-' mon.1 "-" dd.1 /*obtain the constituents of 1st date. */ parse var $.2 yr.2 '-' mon.2 "-" dd.2 /* " " " " 2nd " */ ?.1= '1st' ?.2= '2nd' if _ \== then call err "too many arguments specified: " xtra dy.=31 /*default number of days for all months*/ parse value 30 with dy.4 1 dy.6 1 dy.9 1 dy.11 /*define 30─day months, Feb. is special*/ @notCorr= "isn't in the correct format: YYYY-MM-DD " 

 do j=1  for 2                                  /*examine both dates for correct format*/
 if $.j           ==  then call err ?.j "date was not specified."
 if length(yr.j)==0     then call err ?.j "year"  @notCorr '(missing)'
 if isDec(yr.j)         then call err ?.j "year"  @notCorr '(has a non─decimal digit)'
 if yr.j<1 | yr.j>9999  then call err ?.j "year"  @notCorr '(not in the range 1──►9999)'
 if length(mon.j)==0    then call err ?.j "month" @notCorr '(missing)'
 if isDec(mon.j)        then call err ?.j "month" @notCorr '(has a non─decimal digit)'
 if mon.j<1 | mon.j>12  then call err ?.j "month" @notCorr '(not in the range 1──►12)'
 if length(dd.j)==0     then call err ?.j "day"   @notCorr '(missing)'
 if isDec(dd.j)         then call err ?.j "day"   @notCorr '(has a non─decimal digit)'
 mo= mon.j
 if leapYr(yr.j)  then dy.2= 29                 /*Is it a leapyear? Use 29 days for Feb*/
                  else dy.2= 28                 /*Isn't "     "      "  28   "   "   " */
 if dd.j<1 | dd.j>dy.mo then call err ?.j "day"   @notCorr '(day in month is invalid)'

   yr.j= right( yr.j  +0, 4, 0)                 /*force YYYY to be four decimal digits.*/
  mon.j= right(mon.j  +0, 2, 0)                 /*  "    MON  "  "  two    "       "   */
   dd.j= right( dd.j  +0, 2, 0)                 /*  "     DD  "  "   "     "       "   */
    $.j= yr.j'-'mon.j"-"dd.j                    /*reconstitute a date from above parts.*/
 end       /*j*/

say commas(abs(date('B',$.1,"I") -date('B',$.2,"I"))) ' days between ' $.1 " and " $.2 exit /*stick a fork in it, we're all done. */ /*──────────────────────────────────────────────────────────────────────────────────────*/ commas: parse arg _; do c_=length(_)-3 to 1 by -3; _=insert(',', _, c_); end; return _ err: say; say '***error*** ' arg(1); exit 13 /*issue an error message (with text) */ isDec: return verify( arg(1), 1234567890) \== 0 /*insure argument is just decimal digs.*/ leapYr: arg _; ly=_//4==0; if ly==0 then return 0; ly=((_//100\==0)|_//400==0); return ly</lang>

output   when using the inputs of:     *   2000-1-1

Today   (indicated by the asterisk)   is   2019-10-2 

6,848  days between  2019-10-02  and  2000-01-01

Ruby

<lang ruby>require "date"

d1, d2 = Date.parse("2019-1-1"), Date.parse("2019-10-19")

p (d1 - d2).to_i # => -291 p (d2 - d1).to_i # => 291 </lang>

zkl

<lang zkl>var [const] TD=Time.Date; today:=TD.parseDate("--"); // "yyyy-mm-dd" and variations --> (y,m,d) // or Time.Clock.UTC --> (y,m,d,h,m,s) then:=TD.parseDate("2018-9-30"); diff:=TD.deltaDays(then,today.xplode()); // ( (y,m,d), y,m,d ) println("Number of days between %s and %s: %d".fmt(then,today,diff)); println("Number of days between %s and %s: %d".fmt( 

  TD.toYMDString(today.xplode()),	// to(y,m,d) not to((y,m,d))
  TD.toYMDString(then.xplode()),
  TD.deltaDays(today,then.xplode())));</lang>
Output:
Number of days between L(2018,9,30) and L(2019,9,30): 365
Number of days between 2019-09-30 and 2018-09-30: -365
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