---
title: "How to use tagged_na"
output: html_document
vignette: >
  %\VignetteIndexEntry{How to use tagged_na}     
  %\VignetteEngine{knitr::rmarkdown} 
  %\VignetteEncoding{UTF-8}
---

```{r setup, include=FALSE}
knitr::opts_chunk$set(echo = TRUE)
```

Base R supports only one type of NA ('not available') to represent missing values. However, your data may include several types of missing data or incomplete category responses. 

To address this issue of a singular "NA", we use the `haven` package [`tagged_na()`](https://haven.tidyverse.org/reference/tagged_na.html) 

`tagged_na()` adds an additional character to any NA values, enabling users to define additional missing data types. `tagged_na()` applies only for numeric values; character based values can use any string to represent NA or missing data. 

## recodeflow approach to coding missing data

`recodeflow` recodes missing data categories values into 3 NA values that are commonly used for most studies: 

- NA(a) = 'not applicable' 
- NA(b) = 'missing'
- Na(c) = 'not asked'


**Summary of `tagged_na` values and their corresponding category values.**

| recodeflow `tagged_na` | category value | Label |
|----------------|--------------|
| NA(a) | 6                  | not applicable     |
| NA(b) | 7                  | missing - don't know         |
| NA(b) | 8                  | missing - refusal            |
| NA(b) | 9                  | missing - not stated         |
| NA(c) | question not asked in the survey cycle  |

## Example `haven::tagged_na()`
```{r}
library(haven)
x <- c(1:5, tagged_na("a"), tagged_na("b"))

# Is used to read the tagged NA in most other functions they are still viewed as NA
na_tag(x)
```
```{r}
# Is used to print the na as well as their tag
print_tagged_na(x)
```
```{r}
# Tagged NA's work identically to regular NAs
x
```
```{r}
is.na(x)
```