- NAME
- SYNOPSIS
- DESCRIPTION
- METHODS
- PRINTF DIRECTIVES
- KNOWN BUGS
- BUGS AND QUESTIONS
- SEE ALSO
- LICENSE
- AUTHOR

# 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`

so

`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.

# SEE ALSO

Date::Manip - main module documentation

# 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)