---
title: "Working with vtools: Flexible Variable Selection"
author: "Søren Højsgaard"
output:
  rmarkdown::html_vignette
vignette: >
  %\VignetteIndexEntry{Working with vtools: Flexible Variable Selection}
  %\VignetteEngine{knitr::knitr}
%\VignetteEncoding{UTF-8}
---

```r
library(doBy)
library(rlang)
data(CO2)
```

## Overview

The `v*` functions in the `doBy` package allow for flexible and consistent handling of variable input.
These tools support unquoted names, character vectors, and formulas.

The main functions are:

- `vparse()` – extract variable names from flexible input
- `v()` – shorthand for `vparse()`
- `vselect()` – select columns from a data frame using flexible input
- `vcheck()` – verify that variables exist in a data frame
- `vmap()` – apply a function to each parsed variable name
- `vrename()` – rename variables in a data frame

---

## Examples

### `vparse()`
```r
vparse(Treatment, Type)
vparse(c("Treatment", "Type"))
vparse(~Treatment + Type)
```

### `v()` – shorthand for `vparse()`
```r
v(Treatment, Type)
v(~Treatment + Type)
v(c("Treatment", "Type"))
```

### `vselect()`
```r
vselect(CO2, Treatment, Type)
vselect(CO2, ~Treatment + Type)
```

### `vcheck()`
```r
vcheck(CO2, Treatment)
vcheck(CO2, ~Treatment + Type)
```

### `vmap()`
```r
vmap(~Treatment + Type, toupper)
```

### `vrename()`
```r
vrename(CO2, c(Treatment = "Trt", Type = "Group"))
```

## Summary

The `v*` tools simplify working with variable names and selection in data frames,
making it easier to write functions that accept flexible input formats.