---
title: "Specifying Columns"
output: rmarkdown::html_vignette
vignette: >
  %\VignetteIndexEntry{Specifying Columns}
  %\VignetteEngine{knitr::rmarkdown}
  %\VignetteEncoding{UTF-8}
---

```{r, include = FALSE}
knitr::opts_chunk$set(
  collapse = TRUE,
  comment = "#>"
)
library(ggplot2)
library(emphatic)
```

```{r setup}
library(ggplot2)
library(emphatic)
```

```{r}
test_df <- head(mtcars, 10)
```


The methods for selecting columns works similar to `tidyselect` used by 
dplyr.   This is a bespoke implementation of these selections, and may not work
exactly the same:


| selector | description | example
|---------:|------------:|--------------:|
|`starts_with()` |names of columns start with the given text | `starts_with("day")`|
|`ends_with()` |names of columns end with the given text  |`ends_width("2024")` |
|`everything()` |all columns (the default behaviour)  |`everything()` |
|`all_of()` | **all** of the named columns |`all_of(c('mpg', 'wt'))` |
|`any_of()` | **any** of the named columns | `any_of(c('mpg', 'wt'))`|
|`matches()` |regular expression matches against column names |`matches("day0\\d+")` |
|`contains()` |name contains the given text |`contains("value")` |
|`col_number()` |the number of column | `col_number() == 3` |
|`all()` |select everything |`all()` |
|`n()` | returns integer specifying number of cols |`cols = n()` will select the last column |




Select all cols
------------------------------------------------------------------------------

```{r}
test_df |>
  hl('skyblue')
```

```{r}
test_df |>
  hl('skyblue', cols = NULL)
```

```{r}
test_df |>
  hl('skyblue', cols = all())
```


Select cols by index
------------------------------------------------------------------------------

```{r}
test_df |>
  hl('skyblue', cols = 2:5)
```

Select cols by name
------------------------------------------------------------------------------

```{r}
test_df |>
  hl('skyblue', cols = c('mpg', 'gear'))
```


Select cols by rowname symbol
------------------------------------------------------------------------------

```{r}
test_df |>
  hl('skyblue', cols = c(drat, am))
```

```{r}
test_df |>
  hl('skyblue', cols = drat:am)
```


Select cols using `col_number()`
------------------------------------------------------------------------------

```{r}
test_df |>
  hl('skyblue', cols = col_number() < 4)
```

Select cols using selectors like `tidyselect`
------------------------------------------------------------------------------

```{r}
test_df |>
  hl('skyblue', cols = contains('a'))
```

```{r}
test_df |>
  hl('skyblue', cols = ends_with('t'))
```


```{r}
test_df |>
  hl('skyblue', cols = any_of(c('mpg', 'wt', 'age')))
```