# Introduction to theRefdate

## Overview & Motto

`theRefdate` provides simple date manipulation functions operating on character strings in the format `"DD.MM.YYYY"`. All functions follow this `"LP"`-flavour convention on formatting dates.

simple and fast.

## flavour

Returns the flavour identifier of this package:

    flavour()
    #> [1] "LP"

## jahr

Extracts the year as a numeric value:

    jahr("02.02.2002")
    #> [1] 2002

## monat

Extracts the month as a numeric value:

    monat("14.06.1789")
    #> [1] 6

## tag

Extracts the day as a numeric value:

    tag("03.02.2000")
    #> [1] 3

## dateDiff

Computes the difference between two dates. Returns a list with four elements: `diffJ` (years), `diffM` (months), `diffDauer` (duration as fraction of years), `diffDauerM` (total months):

    result <- dateDiff("01.12.1999", "01.01.2000")
    result$diffJ
    #> [1] 0
    result$diffM
    #> [1] 1
    result$diffDauer
    #> [1] 0.08333333
    result$diffDauerM
    #> [1] 1

## dateAddMonths

Adds or subtracts months from a date:

    dateAddMonths("01.01.2000",   1)   # add 1 month
    #> [1] "01.02.2000"
    dateAddMonths("01.01.2000",  -1)   # subtract 1 month
    #> [1] "01.12.1999"
    dateAddMonths("01.01.2000",  12)   # add 1 year
    #> [1] "01.01.2001"
    dateAddMonths("01.01.2000", -13)   # subtract 13 months
    #> [1] "01.12.1998"