counting years between two dates

**news.west.cox.net** · Jul 23 '05, 03:27 PM

Re: counting years between two dates

> Problem like in subject. There is no problem when I want to count days[color=blue]
> between two dates. Problem is when I want to count years becouse of
> leap years.
>
> For ex.
>
> between
> 2002-11-19 2003-11-19
> 365 days = 1 year
>
> between
> 2003-11-19 2004-11-19
> 366 days = 1 year (leap)
>[/color]

I am not familiar enough with javascript to be able to give you the correct
answer, but I can tell you that you will need to use some sort of date
object.

The date object should have a way of finding the date as it is represented
in seconds since the epoch.

So, you would create two date objects, find their time in seconds since
the epoch, and convert this into a number of days.

In fact I just googled for "javascript date" and the first result has the
answer.

// UNTESTED
var date1 = new Date(yr_num, mo_num, day_num);
var date2 = new Date(yr_num2, mo_num2, day_num2);

var date1_in_second s = date1.parse();
var date2_in_second s = date2.parse();

var difference = date_2_in_secon ds - date_1_in_secon ds
// above is assuming date2 is more recent than date1

//now difference is the number of seconds between the two dates so...
var difference in years = int(difference / 140400)
//this would be the number of days in between the two dates...

**Lee** · Jul 23 '05, 03:27 PM

Re: counting years between two dates

Bambero said:[color=blue]
>
>Hello all
>
>Problem like in subject. There is no problem when I want to count days
>between two dates. Problem is when I want to count years becouse of
>leap years.[/color]

http://www.merlyn.demon.co.uk/js-date1.htm#DY

**RobG** · Jul 23 '05, 03:27 PM

Re: counting years between two dates

Bambero wrote:[color=blue]
> Hello all
>
> Problem like in subject. There is no problem when I want to count days
> between two dates. Problem is when I want to count years becouse of
> leap years.[/color]

I would guess you are having trouble with months too.

The best way is to convert to date objects, then deal with those. When
measuring days, months and years between two dates it is simpest to
add one year/month/day at a time until the earlier date gets to the
later date. The following script doesn't care whether the lower date
is entered first or last, it sorts them out anyway.

The following assumes you have done all that is required to validate
that dates are entered as yyyy-mm-dd. It is tested in Safari, but
should work elsewhere.

Have fun, Rob.

<html><head><ti tle>Date fun</title>

<script type="text/javascript">
function check2k(a) {
return (a<1900)?a -= -1900:a;
}

function addYr(a) {
return new Date(check2k(1* a.getYear()+1), a.getMonth(),a. getDate());
}

function addMth(a) {
return new Date(check2k(a. getYear()),1*a. getMonth()+1,a. getDate());
}

function addDay(a) {
return new Date(check2k(a. getYear()),a.ge tMonth(),1*a.ge tDate()+1);
}

function doDate(in1,in2) {
var x = in1.split('-'),
y = in2.split('-'),
yrCount = 0,
mthCount = 0,
dayCount = 0;

// Convert to dates
var date0 = new Date(x[0],x[1]-1,x[2]);
var date1 = new Date(y[0],y[1]-1,y[2]);

// Make the lower one date0
if (date0 > date1) {
date0 = date1;
date1 = new Date(x[0],x[1]-1,x[2]);
}

// Add years to date0 until after date1
while (addYr(date0) <= date1) {
date0 = addYr(date0);
yrCount++;
}

// Add months to date0 until after date1
while (addMth(date0) <= date1) {
date0 = addMth(date0);
mthCount++;
}

// Add days to date0 until after date1
while (addDay(date0) <= date1) {
date0 = addDay(date0);
dayCount++
}

alert('Years: ' + yrCount
+ '\nMonths: ' + mthCount
+ '\nDays: ' + dayCount
);
}
</script>

</head>
<body>

<form action="">
<input type="text" name="y1" width="100px"
value="2003-12-23">Year 1<br>
<input type="text" name="y2" width="100px"
value="2002-12-28">Year 2<br>
<input type="button" value="Calc years" onclick="
doDate(this.for m.y1.value, this.form.y2.va lue);
"><br>
</form>

</body></html>

**RobG** · Jul 23 '05, 03:28 PM

Re: counting years between two dates

RobG wrote:
[...][color=blue]
> The following assumes you have done all that is required to validate
> that dates are entered as yyyy-mm-dd. It is tested in Safari, but
> should work elsewhere.[/color]
[...]

Forgot to mention, you also need to ensure dates are after 1900.

Cheers, Rob.

**Dr John Stockton** · Jul 23 '05, 03:28 PM

Re: counting years between two dates

JRS: In article <99und.330977$a 85.63670@fed1re ad04>, dated Fri, 19 Nov
2004 14:08:29, seen in news:comp.lang. javascript, news.west.cox.n et
<sean.berry2@co x.net> posted :[color=blue][color=green]
>> Problem like in subject.[/color][/color]

NEVER rely on the Subject line.
[color=blue]
> There is no problem when I want to count days[color=green]
>> between two dates. Problem is when I want to count years becouse of
>> leap years.
>>
>> For ex.[/color][/color]

Don't use abbreviations in languages which are not your own, unless you
have good reason for believing that they exist and you know their exact
meaning.
[color=blue][color=green]
>>
>> between
>> 2002-11-19 2003-11-19
>> 365 days = 1 year[/color][/color]

Actually there are 364 days between those dates; it is the difference
which is 365.
[color=blue][color=green]
>> between
>> 2003-11-19 2004-11-19
>> 366 days = 1 year (leap)
>>[/color]
>
>I am not familiar enough with javascript to be able to give you the correct
>answer,[/color]

Better, then, to leave it to those who do.
[color=blue]
> but I can tell you that you will need to use some sort of date
>object.[/color]

/Non sequitur/.

[color=blue]
>The date object should have a way of finding the date as it is represented
>in seconds since the epoch.[/color]

It is not represented in seconds.

[color=blue]
>So, you would create two date objects, find their time in seconds since
>the epoch, and convert this into a number of days.[/color]

One does not *need* two objects; it is possible to use one twice; or,
for speed, not to use a date object at all. The best solution depends
on the format in which the date is initially available. For example, if
the dates are ISO 8601 YYYYMMDD strings, one can subtract them, divide
by 1e4, and truncate.
[color=blue]
>In fact I just googled for "javascript date" and the first result has the
>answer.[/color]

Indiscriminate Googling for javascript is a *reliable* method of finding
bad answers. A good answer could have been found by studying the FAQ of
this newsgroup.
[color=blue]
>// UNTESTED[/color]

Untested code, even when written by an expert, is almost reliably wrong.
[color=blue]
>var date1 = new Date(yr_num, mo_num, day_num);
>var date2 = new Date(yr_num2, mo_num2, day_num2);
>
>var date1_in_second s = date1.parse();
>var date2_in_second s = date2.parse();[/color]

The date object does not AFAIK ever have a native parse method.
[color=blue]
>var difference = date_2_in_secon ds - date_1_in_secon ds
>// above is assuming date2 is more recent than date1
>
>//now difference is the number of seconds between the two dates so...
>var difference in years = int(difference / 140400)
>//this would be the number of days in between the two dates...[/color]

140400 seconds is one day fifteen hours; that is less than a year. As
the OP evidently realises, the number of seconds in a year is not
constant.

Post only tested solutions, on topics that you have a good understanding
of.

A further problem, for methods based on seconds, would be shown (to
many users) for the differences of some pairs of dates of the form
YYYY-10-28.

For the OP :

X = (Y2-Y1) - (M2*100+D2 < M1*100+D1) // for Y M D numbers

A1 = Y1.split(/\D+/) ; A2 = Y2.split(/\D+/)
X = (A2[0]-A1[0]) - (A2[1]*100 + +A2[2] < A1[1]*100 + +A1[2])
// for inputs YYYY-MM-DD, YYYY/MM/DD, etc.

Lightly tested. See below.

--
© John Stockton, Surrey, UK. ?@merlyn.demon. co.uk Turnpike v4.00 IE 4 ©
<URL:http://www.jibbering.c om/faq/> JL/RC: FAQ of news:comp.lang. javascript
<URL:http://www.merlyn.demo n.co.uk/js-index.htm> jscr maths, dates, sources.
<URL:http://www.merlyn.demo n.co.uk/> TP/BP/Delphi/jscr/&c, FAQ items, links.

**RobG** · Jul 23 '05, 03:28 PM

Re: counting years between two dates

Dr John Stockton wrote:
[...][color=blue]
> A further problem, for methods based on seconds, would be shown (to
> many users) for the differences of some pairs of dates of the form
> YYYY-10-28.[/color]

What is the accepted value for 2004-02-29 + 1 year? Is it 2005-03-01
as the JavaScript date function in every browser I tested returns, or
is it 2005-02-28 as logic might have it (if my logic is consistent with
popular opinion...)

Cheers, Rob.

**Dr John Stockton** · Jul 23 '05, 03:29 PM

Re: counting years between two dates

JRS: In article <41a07bdc$0$257 62$5a62ac22@per-qv1-newsreader-
01.iinet.net.au >, dated Sun, 21 Nov 2004 21:27:24, seen in
news:comp.lang. javascript, RobG <rgqld@iinet.ne t.auau> posted :[color=blue]
>Dr John Stockton wrote:
>[...][color=green]
>> A further problem, for methods based on seconds, would be shown (to
>> many users) for the differences of some pairs of dates of the form
>> YYYY-10-28.[/color]
>
> What is the accepted value for 2004-02-29 + 1 year? Is it 2005-03-01
> as the JavaScript date function in every browser I tested returns, or
> is it 2005-02-28 as logic might have it (if my logic is consistent with
> popular opinion...)[/color]

Note that I wrote YYYY-10-28.

AFAICS, ECMA does not define (2004-02-29 + 1 year) explicitly; but it is
probably implicitly defined as a consequence of the way that ECMA says
that set[Full]Year should work; and likewise for adding a month to dates
too late in the previous longer month.

Note that D = new Date("2003/01/31") ; D.setMonth(1) gives March
3rd, and that will not generally be acceptable.

IMHO, the accepted value, outside javascript, is "Don't know; get a
[signed] ruling from the Boss"; either Feb 28 xor Mar 1 should be
considered acceptable. Somewhere on my site, IIRC, there is code to
handle the case of incrementing by an integer number of months from a
day-of-month not available at the destination ... js-date0.htm#MC .

Those who can read German might like to look at
<URL:http://www.merlyn.demo n.co.uk/zel-82px.htm>
and its neighbours; those knowing Latin see 83 not 82.

--
© John Stockton, Surrey, UK. ?@merlyn.demon. co.uk Turnpike v4.00 MIME. ©
Web <URL:http://www.merlyn.demo n.co.uk/> - w. FAQish topics, links, acronyms
PAS EXE etc : <URL:http://www.merlyn.demo n.co.uk/programs/> - see 00index.htm
Dates - miscdate.htm moredate.htm js-dates.htm pas-time.htm critdate.htm etc.

counting years between two dates

counting years between two dates

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