Ubuntu Manpage: Date::Manip::Delta - Methods for working with deltas

Provided by: libdate-manip-perl_6.60-1_all

NAME

       Date::Manip::Delta - Methods for working with deltas

SYNOPSIS

          use Date::Manip::Delta;
          $date = new Date::Manip::Delta;

DESCRIPTION

This module contains functions useful in parsing and manipulating deltas. As used in this
module, a delta refers only to the amount of time elapsed. It includes no information
about a starting or ending time.

There are several concepts involved in understanding the properties of a delta.

standard and business delta
Deltas can refer to changes in either the full calendar (standard deltas), or they can
refer to a business calendar.

With a business delta, non-business days are ignored. Typically, this includes
holidays and weekends. In addition, the part of the day outside of business hours is
also ignored, so a day may only run from 08:00 to 17:00 and everything outside of this
is ignored.

The length of a work day is usually not 24 hours. It is defined by the start and end
of the work day and is set using the config variables: WorkDayBeg and WorkDayEnd
(WorkDay24Hr may be used to specify a 24-hour work day). The work week is defined
using the config variables: WorkWeekBeg and WorkWeekEnd.

Daylight saving time will have no impact on business calculations because time changes
occur at night (usually on the weekends) outside of business hours. As such, they are
ignored in business calculations.

fields
A delta consists of 7 fields: years, months, weeks, days, hours, minutes, and seconds,
usually expressed as a colon-separated string. For example:

1:2:3:4:5:6:7

refers to an elapsed amount of time 1 year, 2 months, 3 weeks, 4 days, 5 hours, 6
minutes, and 7 seconds long.

normalized
A delta can be normalized or not. A normalized delta has values which have been made
consistent with the type of data they represent. For example, a delta of:

0:0:0:0:0:10:70

is not normalized since 70 seconds is better expressed as 1 minute 10 seconds. The
normalized form of this delta would be:

0:0:0:0:0:11:10

By default, deltas are converted to a normalized form in most functions that
create/modify a delta, but this can be overridden.

sets of fields
When normalizing a delta, fields are grouped together in sets where the exact
relationship is known between all fields in the set.

For example, there is an exactly known relationship between seconds and minutes
(Date::Manip ignores leap seconds, so there are always 60 seconds in a minute), so
they will be in one set.

Likewise, the relationship between years and months is known, so they will be in one
set. There is no known relationship between months and weeks though, so they will be
in separate sets.

A standard (i.e. non-business) delta contains 3 sets of fields:

approximate: year, month
semi-exact: week, day
exact: hour, minute, second

The following known relationships exist:

1 year = 12 months
1 week = 7 days
1 hour = 60 minutes
1 minute = 60 seconds

The following semi-approximate relationships are used to link the semi-exact and exact
fields when required:

1 day = 24 hours

The following approximate relationship is used to link the approximate fields to the
semi-exact fields when required:

1 year = 365.2425

Business deltas differ slightly, Since daylight saving times effects are ignored, the
length of the work day is constant, but due to there being holidays, the length of a
week is not known, so a business delta has the following sets of fields:

approximate: year, month
semi-exact: week
exact: day, hour, minute, second

and the relationships used are:

1 year = 12 months
1 day = length of business day
1 hour = 60 minutes
1 minute = 60 seconds

The semi-approximate relationship may be used to link the semi-approximate and exact
fields together:

1 week = X (length of business week in days)

and the following approximate relationship may be used:

1 year = X/7 * 365.2425

When normalizing a delta, no data from one set will ever be mixed with data from
another set.

As a result, the following delta is normalized:

0:3:8:0:0:0:0

Although 8 weeks is clearly more than 1 month, we don't know the relationship between
the two, so they don't mix.

exact, semi-exact, and approximate deltas
An exact delta is one which every value is of an exactly known length (i.e. it only
includes the exact fields listed above).

A semi-exact delta is a delta which includes the exact fields as well as semi-exact
ones.

An approximate delta can include any of the fields.

So, the delta:

0:3:8:0:0:0:0

is approximate. The delta:

0:0:0:0:30:0:0

is exact. The delta:

0:0:0:1:30:0:0

is semi-exact (if it is non-business) or exact (if it is business).

The term "semi-exact" needs a little explanation. Date::Manip tries to do things in a
way which humans think of them. It is immediately recognized that the approximate
fields are of completely unknown length, and the exact fields are of known length. The
"semi-exact" fields are termed such since humans have a way of looking at them which
is consistent, even if it is not exact.

For example, a day is thought of as the same wall clock time on two successive days,
so from noon on one day to noon the next day is one day. Usually that is 24 hours
(for standard deltas), but if you cross a daylight saving time change, it might be 23
or 25 hours (or something different if a very irregular time change occurs). So where
possible, in a standard delta, a day field will change the date, but leave the time
alone.

Likewise, a business week is thought of as 7 days (i.e. Wednesday to Wednesday)
regardless of whether there was a holiday in there.

signs
Each field has a sign associated with it. For example, the delta "1 year ago" is
written as:

-1:0:0:0:0:0:0

The sign of any field is optional, and if omitted, it is the same as the next higher
field. So, the following are identical:

+1:2:3:4:5:6:7
+1:+2:+3:+4:+5:+6:+7

Since there is no mixing of data between sets of fields, you can end up with a delta
with as many as four signs. So, the following is a fully normalized business delta:

+1:0:-3:+3:1:0:0

fractional values
Fractional fields are allowed such as:

1.25 days
1.1 years

When parsing a delta with fractional fields, the delta will ALWAY be normalized using
the exact, semi-exact, and approximate relationships described above.

For example, for a non-business delta, a delta of 1.1 years will use the following
relationships:

1 year = 365.2425 days
1 year = 12 months
1 day = 24 hours

Since the delta includes approximate fields, as much of the 1.1 year portion of the
delta will be stored in the approximate fields as possible.

Using the above approximate relationships, we can see that:

1 month = 365.2425/12 days = 30.436875 days

1.1 years
= 1 year, 1.2 months
= 1 year, 1 month, 6.087375 days
= 1 year, 1 month, 6 days, 2 hours, 5 minutes, 49 seconds

Fractional seconds will be discarded (no rounding).

METHODS

new
new_config
new_date
new_delta
new_recur
base
tz
is_date
is_delta
is_recur
config
err Please refer to the Date::Manip::Obj documentation for these methods.

parse
$err = $delta->parse($string [,$business] [,$no_normalize]);

This takes a string and parses it to see if it is a valid delta. If it is, an error
code of 0 is returned and $delta now contains the value of the delta. Otherwise, an
error code of 1 is returned and an error condition is set in the delta.

A valid delta is in one of two forms: compact or expanded.

The compact format is a colon separated list of numbers (with optional signs):

Examples:
0:0:0:0:4:3:-2
+4:3:-2
+4::3

In the compact format, from 1 to 7 of the fields may be given. For example D:H:MN:S
may be given to specify only four of the fields. No spaces may be present in the
compact format. It is allowed to omit some of the fields. For example 5::3:30 is
valid. In this case, missing fields default to the value 0.

The expanded format has the fields spelled out in some language specific form:

Examples:
+4 hours +3mn -2second
+ 4 hr 3 minutes -2
4 hour + 3 min -2 s
4 hr 2 s

A field in the expanded format has an optional sign, a number, and a string specifying
the type of field. If the sign is absent, it defaults to the sign of the next larger
element. So the following are equivalent:

-4 hr 3 min 2 sec
-4 hr -3 min -2 sec

The valid strings describing each of the fields is contained in "Delta field names"
section of the appropriate Date::Manip::Lang::<LANGUAGE> document. Refer to the
Date::Manip::Lang document for a list of languages.

For example, for English, the document is Date::Manip::Lang::English and the field
names include strings like:

y: y, yr, year, years
m: m, mon, month, months
w: w, wk, ws, wks, week, weeks
d: d, day, days
h: h, hr, hour, hours
mn: mn, min, minute, minutes
s: s, sec, second, seconds

This list may not be complete. You should refer to the language document for the full
list.

The "seconds" string may be omitted. The sign, number, and string may all be
separated from each other by any amount of whitespace. The string specifying the unit
must be separated from a following number by whitespace or a comma, so the following
example will NOT work:

4hours3minutes

At minimum, it must be expressed as:

4hours 3minutes
4 hours, 3 minutes

In the the expanded format, all fields must be given in the order: Y M W D H MN S.
Any number of them may be omitted provided the rest remain in the correct order.
Numbers may be spelled out, so

in two weeks
in 2 weeks

both work.

Most languages also allow a word to specify whether the delta is an amount of time
after or before a fixed point. In English, the word "in" refers to a time after a
fixed point, and "ago" refers to a point before a fixed point. So, the following
deltas are equivalent:

1:0:0:0:0:0:0
in 1 year

and the following are equivalent

-1:0:0:0:0:0:0
1 year ago

The word "in" is completely ignored. The word "ago" has the affect of reversing all
signs that appear in front of the components of the delta. In other words, the
following two strings are identical:

-12 yr 6 mon ago
+12 yr +6 mon

(don't forget that there is an implied minus sign in front of the 6 in the first
string because when no sign is explicitly given, it carries the previously entered
sign).

The in/ago words only apply to the expanded format, so the following is invalid:

1:0:0 ago

A delta may be standard (non-business) or business. By default, a delta is treated as
a non-business delta, but this can be changed in two different ways.

The first way to make a delta be business is to pass in the 2nd argument to the
function. The $business argument may be a string 'standard' or 'business' to
explicitly set the type of delta. Alternately, any non-zero value for $business will
force the delta to be a business delta.

So the following are identical:

$delta->parse($string,'business');
$delta->parse($string,1);

and the following are identical:

$delta->parse($string);
$delta->parse($string,'standard');
$delta->parse($string,0);

The second way to specify whether a delta is business or non-business is to include a
key word in the string that is parsed. When this is done, these strings override any
value of the $business argument.

Most languages include a word like "business" which can be used to specify that the
resulting delta is a business delta or a non-business delta. Other languages have
equivalent words. The placement of the word is not important. Also, the "business"
word can be included with both types of deltas, so the following are valid and
equivalent:

in 4 hours business
4:0:0 business
business 0:0:0:0:4:0:0

There are also words "exact" or "approximate" which may be included in the delta for
backward compatibility. However, they will be ignored. The accuracy of delta (exact,
semi-exact, approximate) will be determined only by what fields are present in the
delta.

When a delta is parsed, it is automatically normalized, unless the $no_normalize
argument is passed in. It can be the string 'nonormalize' or any non-zero value. If
passing it as a non-zero value, the $business argument MUST be included (though it can
be zero) in order to avoid ambiguity.

So the following are equivalent:

$delta->parse($string,'nonormalize');
$delta->parse($string,$business,1);

input
$str = $delta->input();

This returns the string that was parsed to form the delta.

set
$err = $delta->set($field,$val [,$no_normalize]);

This explicitly sets one or more fields in a delta.

$field can be any of the following:

$field $val

delta [Y,M,W,D,H,MN,S] sets the entire delta
business [Y,M,W,D,H,MN,S] sets the entire delta
standard [Y,M,W,D,H,MN,S] sets the entire delta
y YEAR sets one field
M MONTH
w WEEK
d DAY
h HOUR
m MINUTE
s SECOND

mode business, standard

An error is returned if an invalid value is passed in.

When setting the entire delta with "business" or "normal", it flags the delta as a
business or non-business delta respectively. When setting the entire delta with
"delta", the flag is left unchanged. Also, when setting the entire delta, signs are
not carried from one field to another.

By default, a delta is normalized, but passing $no_normalize as any true value, this
will not be done.

If $no_normalize is not passed in, the current value for the delta (which defaults to
0) will be used.

For backwards compatibility, 'normal' can be used in place of 'standard', both as
$field or as $val.

printf
$out = $delta->printf($in);
@out = $delta->printf(@in);

This takes a string or list of strings which may contain any number of special
formatting directives. These directives are replaced with information contained in the
delta. Everything else in the string is returned unmodified.

A directive always begins with '%'. They are described in the section below in the
section PRINTF DIRECTIVES.

calc
$date2 = $delta->calc($date1 [,$subtract]);
$delta3 = $delta1->calc($delta2 [,$subtract]);

Please refer to the Date::Manip::Calc documentation for details.

type
$flag = $delta->type($op);

This tests to see if a delta is of a certain type. $op can be;

business : returns 1 if it is a business delta
standard : returns 1 if it is a standard (non-business delta)

exact : returns 1 if it is exact
semi : returns 1 if it is semi-exact
approx : returns 1 if it is approximate

value
$val = $delta->value();
@val = $delta->value();

This returns the value of the delta. In scalar context, it returns the printable
string (equivalent to the printf directive '%Dt'). In list context, it returns a list
of fields.

An empty string is returned if there is no valid delta stored in $delta.

convert
$delta->convert($to);

This converts a delta from one type to another. $to can be 'exact', 'semi', or
'approx'. The conversion uses the approximate relationships listed above to convert
the delta.

For example, if the exact non-business delta $delta contains:

0:0:0:0:44:0:0

then the following call:

$delta->convert('semi')

would produce the semi-exact delta:

0:0:0:1:20:0:0

The result will always be normalized, and will be strictly positive or negative (i.e.
all fields will have the same sign).

This function can be used to take an exact delta and turn it into a semi-exact delta
(with a day being treated as 24 hours in non-business mode).

There is currently no support for converting business to non-business (or vice-versa).

cmp
$flag = $delta1->cmp($delta2);

This compares two deltas (using the approximate relationships listed above) and
returns -1, 0, or 1 which could be used to sort them by length of time.

Both deltas must be valid, and both must be either business or non-business deltas.
They do not need to be the same out of exact, semi-exact, and approximate.

undef will be returned if either delta is invalid, or you try to compare a business
and non-business delta.

PRINTF DIRECTIVES

       The following printf directives are replaced with information from the delta. Directives
       may be replaced by the values of a single field in the delta (i.e. the hours or weeks
       field), the value of several fields expressed in terms of one of them (i.e. the number of
       years and months expressed in terms of months), or the directive may format either the
       entire delta, or portions of it.

       Simple directives
           These are directives which print simple characters. Currently, the only one is:

              %%    Replaced by a single '%'

           As an example:

             $delta->printf('|%%|');
                => |%|

       Directives to print out a single field
           The following directive is used to print out the value of a single field. Spaces are
           included here for clarity, but are not in the actual directive.

              % [+] [pad] [width] Xv

           Here, X is one of (y,M,w,d,h,m,s). The directive will print out the value for that
           field (in the normalized delta).

           If a '+' is included immediately after the '%', a sign will always be included. By
           default, only negative values will include a sign.

           'width' is any positive integer (without a sign). If 'width' is included, it sets the
           length of the output string (unless the string is already longer than that, in which
           case the 'width' is ignored).

           If 'pad' is included, it may be the character '<', '>', or '0'. It will be ignored
           unless 'width' is included.  If the formatted delta field is shorter than 'width', it
           will be padded with spaces on the left (if 'pad' is '<'), or right (if 'pad' is '>'),
           or it will be padded on the left (after any sign) with zeroes (if 'pad' is '0').

           In the following examples, $delta contains the delta: 1:2:3:4:5:6:7

              $delta->printf('|Month: %Mv|');
                 => |Month: 2|

              $delta->printf('|Day: %+05dv|');
                 => |Day: +0004|

              $delta->printf('|Day: %+<5dv|');
                 => |Day:    +4|

              $delta->printf('|Day: %>5sv|');
                 => |Day: 7    |

       Directives to print out several fields in terms of one of them
           The following directive is used to print out the value of several different fields,
           expressed in terms of a single field.

              % [+] [pad] [width] [.precision] XYZ

           Here, X, Y, and Z are each one of (y,M,w,d,h,m,s). The directive will print out the
           value for fields Y through Z expressed in terms of field X.

           Y must come before Z in the sequence (y,M,w,d,h,m,s) or it can be the same as Z.

           So, to print the day and hour fields in terms of seconds, use the directive:

              %sdh

           Any time all of X, Y, and Z are from a single set of fields, exact relationships are
           used.

           If the X, Y, and Z fields do not all belong to the same set of fields, approximate
           relationships are used.

           For non-business deltas, an approximate relationship is needed to link the Y/M part of
           the delta to the W/D part and a semi-approximate relationship is needed to link the
           W/D part with the H/MN/S part.  These relationships are:

              1 day    = 24 hours
              1 year   = 365.2425

           For business deltas, the approximate and semi-approximate relationships used to link
           the fields together are:

              1 week   = X    (length of business week in days)
              1 year   = X/7 * 365.2425

           For business deltas, the length of the day is defined using WorkDayStart and
           WorkDayEnd.  For non-business deltas, a day is 24 hours long (i.e. daylight saving
           time is ignored).

           If 'precision' is included, it is the number of decimal places to print. If it is not
           included, but 'width' is included, precision will be set automatically to display the
           maximum number of decimal places given 'width'.

           If 'pad' is included, it may be the character '<', '>', or '0', and is used in the
           same way as printing out a single field.

           In the following examples, $delta contains the delta: 1:2:3:4:5:6:7

              $delta->printf('|%.4Myw|');
                 => |14.6900|
                 1 year, 2 months, 3 weeks is approximately
                 14.6900 months

       Directives to print out portions of the delta
           The following directives may be used to print out some or all of a delta.

              % [+] [pad] [width] Dt
              % [+] [pad] [width] DXY

           The first directive will print out the entire delta.

           The second will print out the delta from the X to Y fields inclusive (where X and Y
           are each one of (y,M,w,d,h,m,s) and X must come before Y in the sequence).

           'pad' is optional and can be either '<' or '>' meaning to pad on the left or right
           with spaces. It defaults to '<'.

           If a '+' is included immediately following the '%', every field will have a sign
           attached. Otherwise, only the leftmost field in each set of fields will include a
           sign.

               $delta->printf('|%Dt|');
                  => |+1:2:+3:+4:5:6:7|

               $delta->printf('|%+Dyd|');
                  => |+1:+2:+3:+4|

KNOWN BUGS

       None known.

BUGS AND QUESTIONS

       Please refer to the Date::Manip::Problems documentation for information on submitting bug
       reports or questions to the author.

LICENSE

       This script is free software; you can redistribute it and/or modify it under the same
       terms as Perl itself.

AUTHOR

       Sullivan Beck (sbeck@cpan.org)