---
title: "Introduction to theRefdate"
output: rmarkdown::html_vignette
vignette: >
  %\VignetteIndexEntry{Introduction to theRefdate}
  %\VignetteEngine{knitr::rmarkdown}
  %\VignetteEncoding{UTF-8}
---

```{r setup, include = FALSE}
knitr::opts_chunk$set(collapse = TRUE, comment = "#>")
library(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:

```{r}
flavour()
```

## jahr

Extracts the year as a numeric value:

```{r}
jahr("02.02.2002")
```

## monat

Extracts the month as a numeric value:

```{r}
monat("14.06.1789")
```

## tag

Extracts the day as a numeric value:

```{r}
tag("03.02.2000")
```

## 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):

```{r}
result <- dateDiff("01.12.1999", "01.01.2000")
result$diffJ
result$diffM
result$diffDauer
result$diffDauerM
```

## dateAddMonths

Adds or subtracts months from a date:

```{r}
dateAddMonths("01.01.2000",   1)   # add 1 month
dateAddMonths("01.01.2000",  -1)   # subtract 1 month
dateAddMonths("01.01.2000",  12)   # add 1 year
dateAddMonths("01.01.2000", -13)   # subtract 13 months
```